Projector technology is changing as fast as flat screen TV technology. If I was you, I'd invest in a really good screen, since this will last you over multiple generations of projectors. A quality fixed-frame screen will run you between $1500 and $3000. If you want retractable or electric masking, the cost will go up a fair amount. Don't skimp on the quality of the screen. Read more on
https://gagadget.com/en/66228-5-best-motorized-projector-screens/I'd recommend against getting a used projector. Not only is the technology changing fast, but you have to worry about compatibility with new content and equipment, and they don't last forever. You'll almost certainly need to replace the bulb in order to get full performance, and will probably have to have it thoroughly cleaned to eliminate the dust that accumulates inside. And you probably won't have any warranty.