A friend modified an old electronic organ to act as a midi interface for his hauptwerk rig for use at home. Works well enough for practice.

I bought mine new, but it is getting old now. Those shiny new ones are looking more appealing. It is great to not get out in the cold and wet just to go practice, so definitely worth the money. I have a friend who bought used and it seems to work fine.

Don't give up on finding a real used chamber organ or smallish used real instrument. The OHS and organ clearing house could be helpful here. This isn't feasible for everyone, but is worth looking into if you have the space. It may cost less than you would think.

I'm having a midi console built right now by Arnold Organs (http://www.customorganworks.com/home.html). Unlike a lot of midi console builders, they manufacture just about everything in-house, instead of just assembling parts. Everything can be customized (woods for the keys, pedalboard style, bench style, etc). Much cheaper than purchasing a small organ (new) if you're comfortable working with Hauptwerk.

If you're ok with Allen keyboards, the local Allen dealer here in Memphis had a MDS-15 in perfect condition for $1,400 last time I was in.

You do not have to spend much on a practice organ. Find a used electronic one in good physical shape (the sound need not be necessarily good), and bear this in mind. If the organ already has MIDI it can be connected to a computer that runs Hauptwerk and/or GrandOrgue. The former has a free version with limited voices, and the latter is free open source, and for both there are available a good number of free sample sets. Just search the Internet. The nice thing about Grand Orgue is that it has a built in adjustable reverb to adapt the sound to your acoustic requirements such as for use with dry samples, instead of having to get additional software for Hauptwerk to do this.
If the organ does not have MIDI, there are kits on eBay that will allow you to have it. Converting an electronic organ to MIDI is not particularly difficult, but it is tedious and time consuming as each key must be wired into the MIDI interface. Most of the original electronics in the organ will no longer be needed once the MIDI is in place.
As for selecting the stops, you can use a touch screen monitor that interfaces with the computer. You would be surprised at how cheap large used commercial ones are on eBay.
In my case, I have a Rodgers 520 connected through its original MIDI to a devoted computer with 256gb SSD drive, 16gb RAM and AMD 8 cpu running at 3.2ghz, with a 22" Tyco/Emo commercial touchscreen monitor mounted on a heavy duty arm that swings near me for easy stop selection. I have sample sets from around the world, and use the built in speakers (or headphones) for the sound. Good quality headphones (such as ATH-M40x) even plugged into the computer would be great because you do not have to spend a fortune on deep sound expansion speakers for those 32' stops. I like the Rodgers touch as it resembles tracker action.

An electronic organ for under $4000.

FINALLY! For goodness sakes, they are just synth keyboards with nice cabinets.
I wonder how far down the price could get pushed if they weren't quite so "custom."

https://www.youtube.com/watch?v=01omJsDCNOE

Wow that's amazing!!! I already have a computer..MacBook Pro. Would it handle those programs?

There are some small organs listed in the current Diapason Classified Ads - if a real organ is feasible for you.

It's nice to have an organ (and piano) at home if space allows. You can practice whenever you want - no need to drive (or walk) over to the church.

Somewhere in the Pacific Ocean is a graveyard of hammond 'organs'. This is not meant to pour cold water (salty or otherwise) on teachermom's apparently valued hammond, but - this is one of the most satisfying tales about simulacra that I have heard ever -

Quite a few years ago I knew an organ maintainance man connected with Wicks who had been in the navy during WWII. It seems that at war's end the military were in possession of hundreds of hammond 'organs' which had been used at chapels and services in the field. With no more use for them they were loaded aboard naval vessels and dumped at sea. My friend always had a particular delight in telling that story.

So, having related this tale, I hope sincerely that teachermom24 and her family continue to enjoy their hammond. No ill will or denigrance to people is intended.

Our Hammond came from a Southern home where the family enjoyed many, many memorable times of "jamming" (don't think that's a Southern word, but it's descriptive) with extended family (very Southern). When the donor was selling his parents' house, he wanted to find a good home for this family treasure. As I said earlier, we had been "gifted" with a small Wurlitzer (reminded me of a scene from the movie, Beethoven) which was good for nothing except a lot of headaches. When we were first offered the Hammond, I turned it down but then we found some friends of ours had a similar Hammond and their children were able to use it for music practice. Since my boys were just starting with organ lesson and one was the parish organist, I thought it might be worthwhile to have it at home. Go ahead and laugh. We are happy to have it for now. In a couple of years, after all my kids have gone away, I may just burn it.

I'm having a midi console built right now by Arnold Organs

When you receive it, please let us know how satisfied you are with it.

https://www.youtube.com/watch?v=Or147RQSBOM

My favorite home set-up. Quite remarkable if you ask me.

For those willing to convert an existing non-MIDI electronic organ to a MIDI organ for use with Hauptwerk or GrandOrgue, here is a video that explains the basics of what is involved, in this case using the Hauptwerk Universal MIDI Encoder. It is not difficult, believe me, but somewhat time consuming because of all the wiring involved.

https://www.youtube.com/watch?v=WIz5CPPxZTA

There are other makers of organ MIDI encoders such as MIPC. Search eBay for "MIDI encoder" to get an idea of current pricing and availability.

Y'all are really making me hope I get a good sale on my house so I don't have to spend my savings on the new one LOL!

A popular method is long paper slips that slide over a whole row of drawknobs or tabs and can be swapped out for different sets. There's one European builder that recently released a console with stops on a rotating cylinder above stop tabs so you can have labels for up to four organs always availble and can switch between them with buttons on the console.

For less than $1,000, it's now possible to put a small lcd screen above each drawknob that would change dynamically based on sampleset. For my console, I just have some pistons and a touchscreen. I chose to put the most money in the keyboards over other comforts.

That's super cool. I share your sentiments, though. Seeing the rotating labels with a bunch of plastic manual keys...nope nope nope. We have rear-fulcrum keys here on the console and, combined with the action/pipe fatigue, everything is slow slow slow.

Just imagine having thousands of them, 1/3rd of which are failing!