might be worth looking into US to UK shipping service Planet Express. You get a proxy US address at their warehouse, where they re-send the item to you - they charge a fee of course, usually just a few dollars but it works out far cheaper I've found as long as you select their own basic shipping (which ends up coming through UPS airmail).
Some shops may not let you use a debit/credit card that doesn't match your 'new' US address but you could get round this using Planet Express's 'shop for me' service. You can also edit the customs declaration, value, repackage the item etc.