A cheap and relatively easy fixed screen is to make a wooden frame with center brace, and then stretch some blackout cloth over it. (pics on my web site if you're interested).
You can get the cloth from most curtain shops, and it's normaly a white cloth one side, and whiteish vinyl the other. It should cost you less than $50 all in. Most people seem to use the cloth side.
I made one as a temporary screen, but used it for almost 3 years! I recently upgraded to a 1.2 gain white screen due to the lower lumen output of my new projector - HT1000. I found a place here in the UK that sold screen material (the same as they used for their own screens) and fitted that over the blackout cloth.
It's obviously brighter, and I now have the bright punchy image I had before. Cost to me was equivalent of $150 including carriage.
Of course cost may be an issue, and the returns in relation to price may not seem worth it - is my $150 screen material 7 times better than my $22 blackout cloth?
No, it isn't, but it is better.
As for grey or white - matt white is fine for a start, depending on the projector, but if it's very bright, and has very grey blacks (lamp projectors produce grey blacks to varying degrees - even at the theater), then painting the wall a light grey will help to reduce the black level, improve apparent contrats ratio, and in comparison to the white screen, may help reduce screen door to some degree (not generally an issue with DLP unles you plan to sit closer than 1.75 screen width away). YMMV. It can also help to reduce ambient light should you not have total light control.
Gloss paint will probably hot-spot, i.e. the center will be noticably brighter then the surrounding image, so is probabaly not a good choice.
HTH
Gary.