Regarding landing fees Boscomantico has said it all.
For handling, in first place you should look in the AIP for each airport if handling is mandatory or not. In a lot of airports it is not mandatory, but if you ask for it to any handling agent they won’t say that to you (obviously).
In second place, if the handling is strictly required, then you should take into account this document from AOPA Spain.
Basically the history is like that: AENA regulates the maximum fee to be charged by handling agents for specific services. When handling is mandatory, only these specific services are required. But if you contact the handling agent they will try to charge you for any additional services (the do the same at the end, but giving it a different name) to avoid the regulated price. Then, when asking for a quote of the handling service one must make clear to the company that only wants the minimum regulated service. They don’t like it at all, and probably will try to bore you with evasives until you pay what they want. But if you stand firm, they will finally accept it. For this reason it is good to do it with some time, not just the afternoon before.
In addition to the AENA airports, in Spain there a lot of other marvelous airports with landing fees in the ranger of 5 – 10 € and no handling at all.
Art has already mentioned a lot of them.
Thanks a lot for the feedback.
The current plan is to do a fuel stop in Southern France (Biarritz LFBZ or Tarbes LFBT) and continue straight to Morocco.
If that’s not possible (weather / headwind) we will go to Granada or Jerez.
Thanks for writing up all the very helpful comments tips on the Spanish airports Aart – very useful!
The price there has I believe gone up several times but is still going to be quite cheap. There is a doc in the Spanish AIP
… which is rather useless as it lists only landing and parking fees. Handling comes on top and it’s almost impossible to research these efficiently.
By the way, here is the AENA document for 2015 (just out).
This is the landing fees table:
So, there are only 7 airports which, based on landing fees alone, are very expensive. Problem is: even from the bottom three categories, many (and a seemingly growing number of) airports now charge steep handling fees (often for zero service).
LEAX does not have customs, so no departures to Morocco..
Granada is really nice and was very cheap. It was so cheap that people just left a load of rotting planes parked on the apron.
The price there has I believe gone up several times but is still going to be quite cheap. There is a doc in the Spanish AIP somewhere which lists the prices.
Great scenery nearby.
Malaga (LEMG) bans VFR during some days, but if you are going VFR you may as well go to La Axaquia LEAX report report which has avgas but I don’t think you can fly there direct from the UK (at the limit of sensible TB20 range anyway, though I did Granada direct from Shoreham – the zero-fuel range is roughly Tangier).
Quote@Aart, we plan to fly to Morocco later this month.
Which airfield do you suggest to use (in the South of Spain) to clear customs?
Malaga LEMG would be convenient, but the handling/landing fees seems to be a rip-off…
I don’t know what your (first) stop would be in Morocco, but assuming you have sufficient range here are the best options. Because you depart to a non-Schengen country you need obligatory handling. Check for prices by calling them, but my estimate is 120 euros for handling/landing. South of Spain is quite near Morocco, so you may even want to negotiate a bit 
Granada (LEGR).
Seville (LEZL).
Jerez (LEJR).
Although it has been a while ago (pre-handling days), I have only been to Granada and Jerez, and they were both hassle-free. Granada has a lot more to offer in terms of scenery (Sierra Nevada nearby) than the flatlands of Sevilla and Jerez. Jerez is closest to Morocco though. You may want to have in the back of your mind that there is a UK-run school in Jerez that operates a large fleet of Diamonds, and they have trained mechanics. Just in case..
France, Croatia, Denmark, the Channel Islands and others. And I am quite sure that I will never visit all their airports.
For Croatia it’s very easy – you only have to visit 7 (Pula, Mali Losinj, Rijeka, Zadar, Split, Brac, and Dubrovnik) because that’s all we have on the seaside 
At that point, it’s the availability of acceptable airports that dictate your choice of destination
Exactly this is the main reason for me to avoid spain. I simply do not like to be ripped off. There are many other amazing destinations here in Europe as France, Croatia, Denmark, the Channel Islands and others.
And I am quite sure that I will never visit all their airports.
