It's virtually impossible to predict an exact figure Andrew, since as some of the following shows, some of the charges are decided on an ad hoc basis. The first extract sections are from a US company's advice to customers:
3.2 Since the introduction of new rules regarding VAT in the EU we have been forced to register for VAT in most EU countries so for all customers in the UK and other European Union countries - VAT is charged at the locally prevailing rate for your country. Documentation is enclosed with the goods to confirm that VAT has been charged and the rate which has been applied.
3.3 Under UK VAT rules, VAT is charged on all shipping costs including Royal Mail.
3.7 Many countries charge duty on goods at the point of import, these will normally be collected by the courier used to deliver your goods - this is a charge levied by your government not by eXpansys and we have no control over it.
This next extract is from the general position:
# Customs valuation
The customs valuation of goods is calculated on 1 of 6 methods. The most often used is the transaction method, based on the price paid for the goods. So if there is a sale of the goods leading to importation, then the sale price is the starting point. To this have to be added freight insurance and other adjustments to arrive at a landed cost. In some circumstances payments for intangibles such as royalties have to be included in the values. Commercial arrangements directly affect customs valuation. Where there is a physical transfer but no sale, or they are leased, rented, provided free of charge, or there is a sale but the price is influenced between related parties, then one of the other 5 methods is used.
# Customs duty rates
The rate of customs duty charged on the customs value is determined according to the tariff classification of the goods from 0% to 25%. The UK Tariff is based on the EC Tariff and in turn on the international tariff coding system covering everything in the world. International trade disputes arise when countries interpret the tariff rules differently! Smart importers use tariff engineering to achieve different classifications with a lower duty rate when planning their product design, or when deciding the make up of consignments.