the value of the goods bares no relevance to the shipping charge, just to VAT/Duty.
Shipping is charged at either physical weight/volumetric weight, whichever is the larger!
Also, if the goods are £150, what was the shipping cost? If you paid the supplier to organise shipping, you must get them to mark the incoterms as DDU, otherwise, UPS will calculate charges based on their UK courier cost (if you were paying in the UK, not at source), even if 'SHIPPING PREPAID' is platered over the invoice.
Yes, it is a bummer, however, it a cost you cannot rally get around!
Sorry to throw in a bit of preaching, but you have made an error that thousands have before you and will after and that is not understanding the whole picture - seeing a cheap price in China and think £'s, but not reallu undertsanding everything that is involved.
On a positive note, you have not made a loss and learnt the lesson at the begginning, which makes you sronger for the future!