Went from a E6750 to Q9550 as well, board had no trouble. Might require BIOS update, but checking it's CPU support list should clear it up quickly enough.
Thinking I might get away with a GTX460 on my current 520W PSU, but it's been in intensive use for almost 2.5 years now; capacitors probably aged quite a bit at this point.
But yeah, 200-250 for CPU, 220 for the card, 60 for the ram (4GB kit instead of another 2GB), then maybe another 120 for PSU and again that for board. Adds up quickly.