Q: I shall be flying from Barcelona airport and will be away for 3 months. Is there anywhere to park for this time without being too expensive?
A: There is a long stay car park at Barcelona Airport, located between Terminals 1 and 2. It is slightly cheaper than the other Barcelona Airport car parks.
If you leave your car at Barcelona Airport for 3 months it is going to be expensive.
Alternatively consider leaving your car in a long term secure car park in Barcelona city and then simply catch a taxi to Barcelona airport from the long term car park. You will save many times over the price of parking at the airport by taking a taxi instead and using a long term car park. One such company offering secure car parking in Barcelona is B:SM. They also offer special rates for long term parking. If you contact them they will give you a quote for how much it will cost.