From my experience last year flying in Spain.
There are three levels of landing fee and parking in Spain. The higest last year for my C150 as 4 euro's landing and 1.1 euro parking a day (Valencia). There was a handling charge at Valencia, but as I had cleared customs at San Sabastian on my trip it was not espensive. The only problem I had was finding the GA terminal at Valencia (I had arrived through the main terminal) - as everybody assumend I was a charter passenger.
As Brooklands said - All flights in Spain require a flight plan. I also found they tended to hand you from one service to another - not always obvious until you called up the suggested service and found they had all your details. Not a bad thing as flying through central Spain there is nothing for miles..... and not many airports.
All the Spainish plates are available on line. In English.
http://www.aena.es/csee/Satellite?ci...=7&c=Page&MO=1
If the link above will not work -
www.aena.es then look for AIP and AIS. You need to register, it's instant and free.
Have a good trip,
Tim.