Hi Wigley,
I got my Tom Tom Go last weekend from GlobalPositioningSystems at £444 and can't recommend it highly enough. I posted a thread on here earlier in the week. It sits ontop of the dash with a windscreen mount and has great 3D mapping and is spot on when navigating. I don't think you would be dissapointed and compared to others on the market and the MINI sat nav is good value. Bonus is you can take it from car to car which I reckon is better than the built in Nav.