I'm over in the US and it's 12:00 midnight here, so I'm too tired to find a converter to change those amounts into US dollars. As such, I'm just completely guessing about how much £60-70 is in US dollars.
Anyway, I'd hate to go exactly opposite of what you said about wanting ATI, the nVidia GeForce FX5700 has proven itself to be pretty good. If that's too expensive, a Radeon 9600 Pro is just fine. Stick a big third-party cooler on it and overclock its pants off. It'll have performance going into the Radeon 9700 Pro range after overclocking!