Some would argue that the cheapest 'good' projector is the Epson 5030 - so $2600 or so.
The real 'good' ones IMO start with JVC's lineup, so $3500, but the RS49 at $5000 (MSRP not street price) is my favorite bang/buck.
Then you move into the luxury goods market, where 10k+ starts getting you premium brand names, Sony 4k projectors, hand-selected JVCs, 3 chip DLPs with professional-level brightness, etc etc. Most people don't play in this league, as our rooms don't need the brightness, and the Runco and Sim2s don't have the CR that the JVCs do. But if you have the $ or need a 200" wide screen, $20k+ is where it's at.
All IMO of course