The 'rip off UK' thing doesn't make any sense - Materials and in particular labour (and therefore salaries) are more expensive here, you can't just take a Euro value in Spain and compare like for like.
Additionally, and I would rarely say something like this but I'll make an exception here...
The building work alone for our single story extension with a part pitched part flat roof was £60k. Now, this was a bit complex and we didn't want to have any supporting steels or beams showing so that bumped up the cost but still I think you're being a little optimistic. If we'd have had a...