So, from what I see, you might be able to reuse the case. That's about it with a computer that old.
If you want to upgrade the CPU, you'll need to get new RAM, a new motherboard, and a new copy of Windows. That's enough to go over your budget right there.
You'll also want to replace the hard drive, as that's near the end of it's useful life. The PSU is in the same boat, so that'll need to be replaced as well.
The GPU isn't listed, but if you haven't upgraded it already, that'll need to be replaced as well.