Coventry, I have one pretty bad fabric shop near me so most of the fabric I have bought has been bought from the US. Yes the shipping charges are expensive so I fill the envelope with as much fabric as it can take.
e.g. a few shops will state that up to 10 yards of fabric will fill a certain type of envelope which will cost around $25 - 30 which is about £17 - 20 (estimate). The cost of buying fabric here in the UK to me is cost prohibitive as its almost double the cost of fabric in the US but if I fill that envelope then I save money.
I guess its just working out how much you can save before hitting that add to cart button
Oh and check out etsy, I think every etsy store I've used bar one have refunded excess shipping fees. And I havent been charged any import fees as yet so I've been extremely lucky in that department and I know some day soon that'll come to an end hah!