It only does the organ sounds, but the Voce Micro B-II module might be worth a look. Don't know how much it's going for these days ... The Micro B-II is supposed to be much better than the Micro B. I may be selling my B-II (I just upgraded to
a Nord Electro). Anyway, between that and say a Roland JV1010 module you'd be set ... but there's all kinds if keyboards out there that are decent for the synthy sounds. But I imagine you'd be looking at about $200 PER MODULE, so that would be over your budget, right?
I've even gained a new appreciation for
my Roland U20 lately, as out of necessity I've had to program lots of stuff into it. I'm actually surprised at the depth of features it has and the quality of sounds I can get by editing them! Since you are asking about modules, I assume you have a keyboard to play them thru already?
FWIW, I've learned that a great piano sound on its own isn't always the one that cuts thru the mix ... the one on the U20 actually works well for how I'm playing it in the band situation. But on its own the piano sound kinda sucks.
Well, enough rambling. Hope there's something useful in it ...