buying with credit card from USA? conversion rate???

[plumAJP]

I am in the UK and I need to buy some parts from the usa.

The price comes to roughly $325 with a whopping $143 for shippinh(which i think is pretty deer).

I would be using a virgin credit card but how do i find out how much i will be paying in GBP, who would have the currency rates? virging or the parts supllier?

thanks in advance

[plumAJP]

how would i find out about import duty? would the supplier know?