used DVDs of Japanese anime on eBay? I bought a collection of Ghibli DVD's for a few bucks each there.
And in my area, Japantown has DVD rental libraries where all the kind of shows that your son might be interested in are available for weekly rental of 50 cents each (that used to be the cost a few years ago when I went there with a Japanese friend to get original episodes of Dragon BallZ videos, but I am sure that the prices have not gone up much). These sources are easier to find when you have a local Japanese contact person because they advertise in Japanese language media and are located in hard to find places. A lot of them sell the DVDs as well.
And if your son is interested in trying out animation software, Studio Ghibli's animation software was just recently open sourced by them, so your son can work on it, join user groups etc.
http://www.wired.co.uk/news/archive/2016-03/21/toonz-animation-software-studio-ghibli-free-download
