What would be the best DSLR camera for under $800 for taking senior pictures?

I am looking for a camera suited for portraits. Some will be in a studio setting and some will be outside. I plan on purchasing a flash, several lenses, and a tripod. I have had a lot of practice with my Sony Finepix S1500 which I use in manual mode, so i feel that i am ready for an upgrade. The pictures i will be taking will be for under privileged high school students that otherwise wouldn't be able to have their photos taken. So although i'm sure they would be pleased with any photo, i would like to be able to present them with the best quality possible.