You might want to see if you can find some Crank Brothers' Cobalt wheels, the 26" ones weigh right at 1500g. They list for over $800 but you might get lucky and find a used set for closer to $500. Only bad thing is they're disk-only.

Also, FSA makes the XC-500 set that's 1800g for less than $600. I haven't tried either of these, just some of the lighter ones I've seen.