no you have it about right, if you check a back with Ryan air you also have to pay for airport check in. Plus as an American you won't have a Visa Electron card so you'll have to pay that fee too. Unless you get a 1p ticket, it is probably going to cost the same as flying BA. Which odly enough charges credit card processing fees for UK residents, but allows them to use a Debit card w/o fee, but doesn't charge the fee for Americans.

I flew EasyJet summer of 07, and it was a lot cheaper, but that was back when they allowed 1 checked bag for free. I am still looking for a bank that will issue a Visa Electron card to Americans. I have found a few non-bank PayPal like services that will issue them, but they charge a lot of fees.