Around £800 - £1,000 (possibly more actually now I come to think of it) in one transaction I think. Intel Q6600, Gigabyte X48T mobo, Arctic Freezer Pro 7 cooler, Enermax Galaxy 1kw psu and (the embarressing bit) 4gb of OCZ ddr3 ram.
I wasn't a member of the forums then and although I did plenty of research on the cpu and other parts, I did however pay top dollar for what was pretty new ddr3 top ram. I'm not even going to admit how much the ram alone cost.