Hi and welcome, The "rule of thumb" I always use is that the cost of living is roughly the same as the UK- in some areas it may be a little cheaper, but others dearer, but its not that much different anymore. A two bed apartment could be as little as 400€ maybe less even?? or a two bedroom villa with pool, land etc could be as much as ..well as you like 2000€ plus??? and of course, when you move to spain you lose your child beneifts which has to be taken into account as well!!!
Jo xxx