Do you want to cycle from Spain to Germany but you don't have a bike or you just worry about the transport and the cost of it? If you are also planning to do your trip in May or June... perfect! You could use my touring bike (Fahrradmanufaktur T100, frame size 57cm) with Ortlieb front and back panniers for free. I would only ask for a deposit you are going to get back when you return the bike in Cologne. You can pick up the bike in Granada (also stay a night or two in my place) and start your trip straight away. Any questions?
Btw: From Granada you can also take a direct bus to Bilbao in case you want to start your trip in the north of Spain.