Woah, you can definitely find the E4 for cheaper I think! I think even the E5 is cheaper than that. I have not tried the E3, but from the impression I've read, it is pretty bassy. The E4 is supposed to be weaker in the bass area.
Still, if you don't mind buying from outside the UK, keep the UM2 in mind. They use same drivers as the E5, are designed to be more confortable, and there is much debate between which sounds better (in order words, it is most likely better than the E3). And you can probably find it for around £150 (a quick look on Ebay shows one for £168 inc. shipping, but I am sure it gets cheaper).
Also worth considering are the
Ultimate Ears. If you look at their custom products, you'll know what I really mean about the budget thing
But their Superfi.fi 5 pro line of product is probably within your budget. I've briefly tried them, and to me, they are worth considering too.