Where did you find "except if"? That's not natural to my ears.Might the OP mean 'except if', which is similar to 'unless'?
Both are correct, but mean different things.
With unless, it means that, if you could take your family with you, you would live abroad.
With even if, on the other hand, you are saying that you would not go to live abroad, no matter what.
I take it to mean that you will go ahead whether or not it increases by 10%.
Not a teacher.
If the price applies to anything up to and including 2200 square metres, why do you need to mention 2000 square metres or 10% at all?