Those prices on MBP are pretty good.
They've got some pretty cheap 450D bodies but you would need to add lenses.
Yes, full frame (EF) lenses are more expensive, but if you start with the Canon 50mm f1.8 (£80), that's an EF, so is fine on a full frame 5D, etc.
If you think you might go full frame at some point, you either start off buying EF lenses or accept that you'll have to replace them with more expensive lenses later.