I can't endorse the paying back part.. When I first started playing bass, my parents insisted that I rent for a while, to make sure I would stick with it. When I did and the "lease" was up on the bass, we turned it in and they bought me a new bass, that cost a pretty penny. They also bought my first electric (used) with amp (used).
It seems like you and your wife are encouraging his musical talents. Honestly, if the kid's been good, getting good grades, does his normal chores... If it's the guitar of his current dreams and he's played that exact one and liked it, I say buy it and surprise him - no strings attached - to the deal that is.
Why the interest in the V?