Very poor thinking. The frame is far and away the most important component of the whole unit, if that's not right, the bike is crap. Put your money into the correct size and type of frame first, even if you find yourself using the bits off the purefix while you save.

I personally think you're better buying a complete bike - best value overall and your budget isn't big enough to really improve things with individual components. The one exception to that may be wheels and if buying from a shop or someone like Wabi, you should be able to swap the stock wheels for something better without having to pay full price for the wheels. You could also contact Scrod and ask him to quote you on a complete bike.