I'm currently running on-board graphics and looking for a GPU that's compatible with my setup. I don't want to spend any more than is needed. Maybe ot's not needed at all, I just like having a GPU in the box.
Use will be workstation, streaming, very light CAD work and general purpose stuff.
ASUS H87m-PLUS (Intel HD 4600)
i7 4770 @3.4GHz
Maybe if you want the option for in example gaming purposes something like the R7 260x would be nice for that budget. Also HD 7770 (cheaper) and 7790.. And as a bonus they have amd app acceleration which takes stress of from cpu to gpu. But before bying make sure your power supply is good enough.