A.S.
Ok... I'm going to be the devil's advocate here.
I am the one with the 'hobby car'... Have you considered learning something about cars WITH him?
I know if he wants this all for himself and you tell him that you want to be out in the garage with him to learn some things about rebuilding a car, he won't want to do it anymore. : )
When he asks why you want to learn, tell him that you think it would be a good way to spend time together and give you a hobby too.
I haven't spent a lot of money on my project car... There ARE ways around that.
And depending on what kind of car he's looking for... I can tell you what you should say to 'curb his interest' in this hobby. : )