The cheapest 1080p projector is the viewsonic pro8200 at 799(720 at newegg right now), the refurb was available for under 500 but there hasn't been any more for awhile now.
Even the 720p projectors are hard to find for under 500. The h5360 is 510 at newegg and it often goes on sale with a 50 off code. The other right now is the 705hd refurb which is 439 on the epson site. Some LED units are also around 500, like the PLED w500, although the price is up right now, was down to 399 for a short time on ebay via tigerdirect.