Special interests

Hi, 

My son is 10 year old and has been interested in Lego for a long time. We have a lot of Lego at home but he is always asking for Lego sets, very specific ones which are very expensive. I want to encourage his creativity but can’t afford to keep buying sets. Is anyone aaware are of a place to buy cheap ones or can suggest how to encourage him to be a little general in demands. 

thanks