Well, a good fortron PSU will be 50 bucks at the most. Never EVER use the PSU that comes with a case. That leaves you with 75 dollars to pick out a case. DO NOT get a case that you really don't like that much just because it is cheap.
SLI is up to you. We here at TF don't think it is worth it, because the mobos are more expensive and even if you add another videocard it doesn't add enough performance. Even if you don't get a SLI mobo, you will need at least 125 for the mobo alone.
Antec Super Lanboy
AMD 64 3800 S-939 Newcastle
MSI K8N Neo2 Platinum
1.5 GB pc 3200
WD 160 GB IDE
Viewsonic 22\" Widescreen 1680x1050
Coming Soon: Athlon 64 4000 San Diego/Z-5500/G7/Vista