I'm going to give you an idea that I think will be much better.
Go onto Craigslist + find someone selling a desktop system. Be very picky on the powersupply and case. Everything else you can choose to upgrade later.
I haven't looked at a dell lately, but several years ago, their cheaper desktops were cases that were highly custom to hold very cheap parts that were not interchangeable. Eg, no room for high end video cards, or better power supplies.
This way you can start out with something at a decent price, but able to expand it later.
EDIT: I'd recommend an mid-sized ATX case with the newer drive bays that allow you to snap in drives without screws + where power supply is at the bottom.