[tonyvdb]

Seriously painting on a screen is a very easy task and can be done for under $75.
If you must go with a screen look used I see many pull down screens for $50 or even ask the I.T. department at the College if they have one that you could buy off of them. I work at a university and we always have lots of unused screens that would do the job nicely and give you a good 72" 16:9 image.

 

[tonyvdb]

How about this screen then, its in your area I believe. or This one
Here is another one

 

[tonyvdb]

The window in your room How large is it? Could you build a simple plug for it out of a Styrofoam insulation panel that you can buy from a local Home depot?

 

[tonyvdb]

That is a fairly good sized window, Maybe building a 1x1 frame with black cloth stretched across it would block out enough light to work.

Mech is the best guy to ask about the screen properties :T I'll just let him handle the other question.