My son loves loves loves the sets he got for Christmas. We designed a
Lego table for him and added storage to his room this Christmas as well. Each lego set has it's own bin with a picture of the set on the front. All manuals are stored in a Binder with plastic sleeves. We keep the boxes as well. The whole idea behind this was for a few reasons.
1. A great space to play
2. The pieces won't get all mixed up, lost and spread all over the house making him unable to build the sets
3. Once he's older and tiring of the Harry Potter stuff, we can use something like Craigslist to make some of the money back towards a new series (Starwars or whatever). He doesn't have to sell them. Just if he gets bored with them.
This whole idea was a way to take the sting out of what amounts to hundreds of dollars (if not more) for a hobby.
So far it is working perfectly.
I am in Canada but live close to the border. Before Christmas Target had the best prices I could find ANYWHERE on the castle. I paid just under a hundred for it with a sale and a coupon. It was 150 almost everywhere here. So look there first.
The sets have been well worth it. We have Hogwarts, Hogwarts add on, Quidditch Match, Forbidden Forest, The Burrow, and the Hogwarts Express. The next big one he will want is Diagon Alley. That was sold out everywhere around Christmas though.