As regards import costs, you can easily work out in advance what it will cost using the HMRC website, which has a list of goods categories. It’s 20% of the declared value in Import VAT plus the Customs Duty (which varies depending on category of the item, around 2.5% at most) plus about £12 fee to Royal Mail for paying the fees on your behalf.
For reference, a $279 pedal + $35 shipping cost me about £308 all in, though it depends on the exact exchange rate, which you can also look up.
I haven’t ever had chance to play an OC-2 yet.