B.B.
Check into Lowes and home depot building kits... I don't think they will send it to you, but you can buy thier build and grow kits (kids workshop kits) for about $7.- here...
Also I know that there are curriculum courses for day cares that will send you a months worth of crafts with supplies... Cost is PER child... So if you enroll one kid... thats all you pay for... places like http://daycarekits.com/index.html ... Not sure the age of your son... But they have things out there for all ages...