My basement HT "screen" for 10+ months was simple primer over drywall.
Can't get much cheaper than that.
I used that to evaluate size, different materials, etc.
You read all the reviews here/others places, but how can you get a gut feel yourself?
Visit dealer showrooms. Visit other people (hard to do, is it awkward to just ask someone "I want 20 minutes of your time?", etc)
For value screen, go to the DIY screen section, look for the easiest/value paint mix and try that on the wall you are thinking to use, if you can.
For $3k PJ budget, ok, my brother In-law Epson 7500 UB totally blew me away 4 weeks ago, check that out @ dealer/somewhere. it's got enough kahunas for about any size basement screen you'd have. Lot of PJ's out there.
Just for memories, heres my PJ in room while we were evaluating screen sizes early in my build, actually fun to do.
Too big, but fun to shoot such a huge image on the wall.
Screen image @ about what we settled with.
I used my laptop for DVD's, but also watched HD clips via Quicktime.