The most I've ever spent was 400 quid on a S3 Vision 968 - and it didn't even have any 3D acceleration (it was a professional card with certified drivers and the best option for multi platform use at that point - it even supported multimonitor if you had two of the cards! A month later the Matrox Millenium came out and did more for half the price..)
Next was probably a Voodoo2 almost on launch day and then two fanless Fatal1ty 7600GTs for silent multi monitor at 100 quid each. My refurb 8800GTX was only 50 quid off ebay.
When I upgrade I expect to pay in the region of 150 to 200 quid, so I can run recent games at top resolution. Currently have too many games to play through. Fallout 3 and Gothic 3 are probably the most graphically intensive games I have, and I've not even taken them out of shrinkwrap.
PK