[font color=\'#000000\']There is no way one could provide you with a reasonnable answer without knowing what you want to do with the camera.
Is your main focus landscape? Is it wildlife? Do you want to take images of your friends or of your son's indoor basketball game?
It is probably possible to find a second hand MF setup in good condition (old Pentax 645 with a 80 mm lens) for around 1000 US$, but you shoudln't forget about the price of the film and processing.
Besides what can you do with your great 6*45 Velvia slides then?... Do you want to scan and print yourself? There are no cheap medium format scanners that deliver a quality significantly higher than that of a 6 MP DSLR. You would have to spend a lot for that too.
Considering your budget, I would either go for a good second hand film SLR (Nikon F100 + 24-85 AF-S for instance) or for a digital camera like the Minolta A2 if long is really needed, or Coolpix 8400 is overall flexibility is key.
Best regards,
Bernard[/font]