If you haven't owned , driven and insured the car in the country it is coming from, then you will have to pay:

Cost of car and handling at port plus cost of shipping to U.K
Add 10% import duty (unless its a truck then 22% I believe)
Total that and add 17.5 % VAT
Add cost of unloading and storing at docks whilst the paperwork is done.

If its under 10 years old then SVA applies, with some concessions, for US vehicles, eg non folding mirrors.
If its a Jap built car ESVA applies.
If its over 10 years old just MOT.

Makes no difference if you are a trader, C & E want their cut of what you are saving.
( and it has to be realistic value as C&E deal with thousands and have resources to get a true valuation)