A new Netflix like service through a company called Pley.com allows parents and kids to rent LEGO sets for a monthly fee and return it for a while new set the following month. This service can save you hundreds of dollars or more a year and allows your child to enjoy the fun of building a new set each month, rather than having to buy a whole new set.
The service costs ($15/month), medium ($25/month) or large sets ($39/month).