Importing from the USA doesn't really make sense at the current exchange rate of around £1 = $1.50.

Many American companies like to use Fedex or UPS, whose charges are outrageous - maybe $50. US Postal Service is just as good, and much cheaper.
There's VAT (sales tax) to pay at 15% on the total price, including shipping. Possibly import duty at around 3% as well.

There's also the carrier's "handling charge" of £8 to £15, which they charge for collecting the VAT from you and passing it to the Tax Man.

If you pay by credit card, there'll also be a commission fee for paying in dollars. This is normally hidden by the card provider offering a worse exchange rate that the quoted rates - another 2% or so.

It could end up costing £330 - same as the UK price.

I've bought many items from the USA, and it was worth doing when Sterling was around $1.90, the seller used USPS, and was OK with declaring the item as a gift worth less than £36.