When I first started in 2010, this was to chase a deposit I had made way back in 2004, there was little hope to be honest. There was a law that said the banks and developers were responsible and should return our money if the property was not built, but not many cases had enforced this law.
The banks made the most of this by refusing to pay and going to court to defend themselves. However Ley 57/68 in Spanish Law makes it clear that they are responsible. Many people, like my group, decided to take on the banks and developers on this basis. It took time and a lot of work. However, in the end we started to see some successful cases and this has set new legal precedents making it possible now to get your money back where it was not possible in the past (to be realistic about it).
This has however lead to many lawyers jumping on the bandwagon and many middle men too taking a cut of the return of your deposit money.
It is a legal industry in Spain now a bit like we have had PPI in the UK, albeit on a smaller scale of course as not as many placed deposits on off plan property in Spain as they took out PPI on loans and credit cards in the UK!
But the same has happened. And, just like PPI, you can get a lot of it back or a little depending on how you go about it. You can give a lot of your money away or a little. Its largely up to who you elect to represent you.
Therefore have some great hope that you can get your money back (although each case has to be assessed on its merits of course) and be careful as to how you choose your lawyer. Make sure you fully understand their fee structure and compare to others. The main thing however is to get a lawyer that can achieve success as even 100% of nothing is nothing!