For instance, Senior Rails or Symfony Backend Engineer market salary is around 45K € [1]. I've seen job offers at the job board I maintain (www.jobsbcn.com) offering up to 70K€ salary for these positions.
Nevertheless, it's not all about the money, flexible working hours and many other perks are also offered at many Startups.
Also, working next to the beach and having a swim at lunch time (I've been working in one of those companies...) or being less than a two hour drive from ski resorts is a plus you cannot disregard, specially if your city of origin does not offer these qualities.
[1] Please, let me clarify that 45K is not as much as you would be paid in Berlin. Also, housing is cheaper there too. But those are different cities with different things to offer.