I don't know much about Electribes, but I can help you with the keyboard. $600 isn't an incredibly high budget... but it should be enough to get you something fairly good. First of all, I'd suggest looking to buy used.... check eBay, pawn shops, and the classified ads... you never know what you'll run across. Usually, if you find the right places to buy from... you can get a board in mint condition for well under the price it would be if you bought it new. Here's a few boards to check out....
Roland RS-5: It's a 61-key board with sounds derived from the XV soundset. There's plenty of sounds and plenty of ways to mess around with them. The best part is, the RS-5 only costs $700 brand new. If you can find one used, I bet you could get it for about $500-600.
Novation K-Station: This is a more exotic keyboard. It only has 25 keys. But that's because it is made more in the style of a virtual analog keyboard rather than a digital sample-playback synth. It basically does nothing but "synth sounds and crazy effects." I've never used it, or heard anything about it..... but at $700 new, it can't be all that bad. Check it out.... but only if you're into that sort of thing.
Korg MS2000: This is another VA synth, like the K-Station. I'd be willing to bet that's it's a little better than the K-Station, simply because I've actually heard some good things about the MS-2000, and I've messed around with it a little. Korg also has a great reputation. Anyway, the MS-2000 has 44 keys, and about all the knobs and buttons you could ever want. It goes for about $750 new.
Yamaha S-30: Ok, now we're back to "normal" synths. This is basically an S-80 with less keys. In fact, I think the only difference between the two boards IS the keybed itself. The S-30 has great sounds, but won't have as many weird sounds as the K-Station or MS2000. However, it does have great piano, electric piano, and string sounds.... which neither of the two VA synths will have. The S-30 goes for about $800 new.
Ok, you may have noticed that all of the keyboards I mentioned are about $100-200 above your given price range.... this is why I told you to look for something used. Honestly, the RS-5 is about the cheapest keyboard I would consider buying if you're looking for something more "real" than the typical Yamaha PSR or Casio. Either consider raising your budget a little, or look for something used. Personally, I'd look through eBay and see what kind of prices you can get on these boards.
BTW, you can find info about all of these (and many other synths) at
www.musiciansfriend.com
Hope this helps. If you have any more questions, feel free to ask!