Oddly enough, there's very little difference. I just looked into the USPS website @
www.usps.com and the postage for a parcel weighing two pounds shipped to the U.K. via Express mail (automatically insured for $500.00) would be $28.75 USD. Airmail parcel post for the same parcel would be $26.60 including the added cost of $500.00 insurance, and oddly enough, parcel post via surface mail is the most expensive of all @ $29.60, again insured for $500.00 (Insurance for $500.00 is $6.60) The cheapest option is economy letter post (surface mail) @ $6.30 but insurance is not an option with this method, although it can be registered for an additional $7.50 for a total of $13.80 and, if registered, you can only collect a maximum of $40.45 if it should become lost. Though because of this, you only need show a value of $40.45 on both the customs form as well as the registered mail form. In any case, it's not a good idea to have anything showing the full cost paid for the item included with your parcel should customs decide to inspect the parcel. Some sellers may be reluctant to help you dodge the Queens tax collector, but it doesn't hurt to ask.