Where do you guys buy your aluminium for machining?

I'm after some offcuts for practising with, eBay is usually my go to online store, but most on there seems pricey. To the point where I couldn't buy the raw material for the same cost as a fully CNC machined part from the USA including shipping...

I'm in the north west England, and can travel for a good supplier.

I have a local steel stock holder, but want to start on alu.

Would welcome any pointers please chaps.