Last year we forfeited a 'proper holiday' and bought Merlin Passes. For 3 of us (Noah was only 2) it cost us about £300. So we made the most of them.
We went to:
Legoland Windsor (1 and a half days). post 1post 2
Alton Towers (2 and a half days) post 1post 2
Legoland Manchester (4 times - I think) post
Sealife Manchester (2 times)