Several points here:
1. Low cost LH (or BA) flights between London and Frankfurt seem to be a thing of the past. I used to fly out on Friday nights and back on Monday mornings on LH, then it became impossibly expensive. "What happened to the advance booking cheap seats?", I asked. "Ve still haff them" I was told. But I selected 20 dates at random and on not one was there a cheap flight from London Airport (LHR) to Frankfurt and back. "Vielleicht the flights from Stansted cheaper being are" said the person with whom I spoke. So I loked up Stansted flights to Frankfurt - and discovered buzz were far, far cheaper. Plus you could buy a drink when you wanted rather than being force-fed a Lufthansakaesebroetchen at top of drop if they'd finished pandering to the fat @r$es in Business Class. The buzz cabin team are so much friendlier than either the clinically efficient LH ladies or their gel-haired pretty boys who make my flesh creep.
2. Ryanair do NOT fly to Frankfurt. They fly to an ex-military aerodrome called Hahn which is BŁOODY MILES from Frankfurt - a long bus or train ride (which takes even longer than the flight!) is then needed to get anywhere close to the city.
3. Quite frankly LH are too smug and rely on their business traffic whilst Ryanair are rather imaginative in describing their Hahn flights as flights to Frankfurt. In my opinion the only airline to have got it right is buzz - and thanks to them I'll be off again over the New Year to see my ladylove once more!