Upvote:2
Sort of a match for what you're looking for: http://adioso.com.
Upvote:2
More of an answer to your secondary request, but FlightChecker by MoneySavingExpert is my go-to tool for 'flights under £X' using low-cost carriers to European destinations (either a specific place, anywhere in a given country or simply anywhere in Europe), within a range of dates or on specific dates.