If you're going for strictly Hammond sounds, you can't beat a vintage Hammond organ.
B3s are certainly the most expensive, but C3s are a little less, but the SAME instrument. An A 100 is the same as a B3 and C3. It has internal speakers, but does have a speaker out connection and is less expensive than the B and C.
One organ that I don't hear too much about is the E-111. You can get one of these for less than 1000 dollars. This was my 1st Hammond, and I traded it to a studio for recording time. They were made in the late 60s, and should not be confused with the prewar Model E, which is another kind of organ all together....
Drawbacks-cheesy percussion, one set of drawbars per manual, does not have the left hand keyboard presets, but these annoying tabs, and top heavy-becareful when moving, also has the 'diving board' keys rather than the 'waterfall keys that most other Hammonds have.
Pros-has great chorus and vibrato, reverb, cost, internals and sound is the same as a B3, full size pedals. B3 percussion is available from Trek, and this percussion system adds volume control to percussion at your console rather than just loud or soft.
If you're looking for a smaller unit, the Hammond XK3 is really where it's at. The features are incredible. Did you know the key click on the new Hammond organs is not synthesized, but is actually key clicks caused by the contacts for each of the drawbars? Thats just like the original Hammonds are. The XK3 also has the same kind of presets the b3 has, the flipped keys. The panel on the Xk3 is very close to the real thing. Two of these stacked would look like a real organ. That's my dream set up.
The biggest advantage the Nord electro has over the xk3 is that the nord has a lot of vintage keyboard sounds besides the Hammond. Some people might be put off by the drawbar situation on the Nord, but after having spent some time with it, I really like it-check it out and see what you think. Also, additional Nord sounds are downloadable from Nord'a website directly to the Nord.