Edited to add.
I was in a similar solution to you earlier this year (I had 2 properties in Spain). I sold one of them by offerring it to market and a large discount (below my outstanding mortgage) and it sold very quickly. I did not use an agent
My selling costs were 800 Euros (the price of a solicitor I used). (He was really useless but that is another story)
Have a look a http://www.fotocasa.es you can advertise for free. It’s a very good site. If you market your property at the right price it will sell. Don’t follow the market down like everyone else. We are probably 2 years away from the bottom.