In my opinion, it really doesn't make sense to try and save too much when it comes to music instruments. You usually get what you pay for...
Good instruments can always be found used in good condition for half of the price they cost new. I'd be looking around for something like a used Roland FP-7. You can't go very wrong with Roland, Yamaha, Kurzweil, Kawai... just don't buy their cheapest products (as with all music instruments).
If you don't need built in sounds, look for a master keyboard (you control sound modules with them via MIDI (your computer for example)... however, i have no recommendations there, as i found most new ones that don't cost a fortune are cheap plastic keyboards (Akai, M-Audio), so i ended up getting a used Yamaha KX-88 which is built like a tank (regarded as one of the best master keyboards out there, was Ray Charles favorite they say... but quite hard to find one).