I would agree with the comments of the last poster, be very careful moving into this market as it is certainly saturated and €300 for keyholding given the number of local people that provide these services, seems high
Often owners will use a local person, that can provide a good service and that can work for less as they are often not legal, perhaps retired and doing this for extra money
Most of the rentals I get for my property in Villamartin I get form the large rental websites that pay a lot of money to get traffic to their site like Holiday Rentals and Daltons and expect to spend money on ogoing SEO optimisation
Are their similar organistions offering local rental advertising yes, loads, every local paper, shop window plus management company but nobody guarntees rentals
Airport pick ups can be a problem as you cannot normally get the required insurance to do this legally
My advice come over and do your own reasearch