Hey Gabe,
M-Audio has the best collection of keyboard controllers that I know about. They also sell at least two 61 key models. The axioms also have lots of MIDI assignable pads and buttons since you won't have pistons. They are hard to beat pricewise. You can find loads of discounters on ebay. Don't forget about Roland (Edirol) too. They have three 61 note models.
What you will probably end up missing in the M-Audio products is the feel of the keyboards. Typically, you either get a piano weighted or semi-weighted action or else a really light... spongy feel. If you're cool with that, then the controllers will work fine. The CMK2 keyboards have a pretty firm feel to them with a slight "tracker" release as you depress the key. That is fairly useful for repertoire where you are working on precision (i.e contrapuntal)
A couple other things you might miss are the piston rail and that they stack in a compact way. Since you are on contrebombarde already, you can use the "find an instrument near you" and try out different hardware from different Hauptwerk users near you.
Other options for keyboards:
See if anyone in the Hauptwerk community has stacks of our older CMK1 stacks. Maybe they are looking to upgrade. Then you will have the stacking and pistons if not the tracker feel
If you don't mind wiring, you can probably find some nice, used organ manuals. Typically, they feel really nice to play and have wooden cores etc. We can always help you with the scanners to bring them to life.
Keep in mind that you can always acquire the manuals one at a time over time as budget permits. This way, you don't spend $300 on an interim keyboard controller and then another $720 ish (US) to upgrade later.
Anyway, those are some ideas. If you have any other questions about our products, you can always email me at midisales at organworks.com