There's two ways to look at the price game
1. You buy a project that's so crappy it should have been free.
You spend the same amount of money just to get it to the point the more expensive one was already at.
This method, more times than not, ends like this, your son loses interest, you're tired of it and the next guy benefits from your labor and money because, he gets the deal.
2. You spend more money up front for a good starter, you and your Son enjoy the build all the way through with a great experience, joy rides and car shows.
Beside it sounds like times a waisting and you're eager to get started [dr
After example two is done, you get a more serious father son project then, run around picking parts up in the first father son vehicle
Just my humble (experienced) opinion