I need help with my studio treatment (check out the 3D!)

I didn't get any responses before so here's a better image... This is a project studio for a CD I'm doing myself and occasional demos for other bands. I need it to sound decent enough for vocals, guitar and mixdown. Just one room, no booth or anything. The room is already finished and I just want to add the sound treatment. I don't have $$ to redo the walls or anything. I plan on spending $500-$600. Will this sound decent? The bookshelf and curtain are just ideas for diffusion and a bit more absorption. Any suggestions?