I am thinking of buy the KAAZ gerset from the US they qoute me $3,000 dollars to my door. What extra costs would the Customs in the UK stick on as well?

You'll have to pay import duty and VAT.

From the Customs and Excise website -

"Import duty is a percentage of the value of the goods and can vary according to the nature of the goods and their country of origin. It is charged on the declared value of the goods - including any local sales tax - plus postage, packing and insurance costs. VAT is added at the same rate that would apply to the goods in this country. In addition, the freight forwarders may charge a fee when the goods are delivered. This is levied by them as a contribution towards their costs and is entirely separate from the duty and VAT charged by Customs."

Dave.