Cheap shipping to return fabric to UK?

Don't use UPS -

USPS Priority should be around $35, and the basic service should be ~$20ish (no tracking #)

I don't think he meant total. If its more than 4 pounds I think you have to use priority international. Less than 4 pounds will be cheaper.

Not total - $35 if you ship Priority w/ limited tracking, $20ish if you ship First Class International with no tracking.

I would opt for USPS and avoid any other couriers. I paid something like $36 last November to ship a 4.5 pound package to UK, IIRC.

I think you would need to label the package clearly (to avoid VAT problems for the merchant) but I'm sure they've already told you about that. Do they charge extras for re-stocking and second time delivery? Depending, you might want to see if you can re-sell the fabrics to a buyer closer to you first and use that money to pay for newer fabrics.

Did you buy them via mail order? I am curious as to why you might be wanting to exchange the fabrics because unless you see them in person, I don't know how exchanging them can ensure that you get the fabrics you really want in the second or even third try. This might turn out to be a costly shipping exercise. If possible, it's better to ask for small sample swatches mailed to you first.