Are you a handy man? If so you can build RCM that will work every bit as good as a VPI and for a lot less money. It is pretty simple and it would be another great project to work on with your son.
Check out this page.
http://www.teresaudio.com/haven/cleaner/cleaner.html
Check out this page.
http://www.teresaudio.com/haven/cleaner/cleaner.html