Sorry to be so dense, but I just want to be sure I have it right:
1) Buy one-way ticket SFO to London
2) Buy one-way ticket London to another European Country
3) Buy one-way ticket from another European Country to SFO
Thanks!
Duh-nise
Not Exactly. What is better is to get an "Open Jaw" (Arrive one airport, leave from another eg Arrive Heathrow, Leave from Dublin) which is usually cheaper than two one way tickets. Then you use a LCC to get to the going home airport city (which may be another airport from the LCC or not).
That's probably the cheapest in monetary cost, but with the additional fees and hassle associated with LCC's, it might not be worth it to you. Since you want to spend the whole week in London, I would just get a RT SFO-LHR/LGW/etc. and curse PM Gordon Brown on the fees.
If you do decide to try a LCC, I would plan an extra travel day just in case there is a delay so you don't miss your return home. If there is no problem, you have a day to see a new city, something always worth while on a European trip.
If you have the time and energy to try some combinations, check
www.whichbudget.com for some ideas on LCC and routing.
I have used LCC many times in Europe, primarily to get to where I want to go after getting FF tickets to someplace I did not want to go. It can work fine or it can be a pain. This August, I got an Open Jaw Arriving London and Leaving from Venice. I used BMI on one of their really low fares ($30) to get from London to Venice. Another time, I flew into London and home from Amsterdam (which also has some departure fees now BTW) using BMIbaby on a 1 Pound fare between London and Amsterdam since I could not get a return from London on my FF ticket when I needed to return.
Enjoy London. Its one of my favorite cities and I am leaving tomorrow for another visit.
Cheers