catfish, I think you are looking in the wrong places, unless you confused 5970 with 5870. I live only a (well, not so) short swim away from the UK, just across the channel, and 5870s are going really cheap here. With some luck you can buy them second hand for ~120-130 euro, often still covered by warranty. Look in the forums of large gaming communities or whatever your local equivalent of craig's list. And just dont offer the asking price, offer 120 euro (whatever that is in pounds) and you might be surprised how many sell. If you really meant 5870s, if you want I can try and find and buy some here and send them over if it turns out they are cheaper here. Shipping is like 18 euro.
I do agree that 5850s are also great choices though. Per "pound" they are usually better deal than 5870. Per watt it will be damn close I think. But perhaps the best thing about them is that they are substantially easier to keep cool. I only have 1 5870 (reference), but damn, it was a hot card until I put a massive overkill cooler on it. Dont know if they are all like that, but if they are, Id rather stick with 5850s