"I see I can buy a back half car for that much....."

You can buy a car for way less than it costs to build one unless you do all the work yourself. Way less.

10k might get you a half decent back half done. Depends on what's included. CM or MS? Nice, detailed, well designed cage and chassis or bare minimum ERW kit with 2x3 rails? Junkyard Dana or good 9"? Quality disc brakes or some old drum brakes that somebody had laying around? Fuel system? 4 link, ladder bars, anti-roll? Good shocks? Sheet metal finished? Plumbing, wiring, battery mounts? Does the builder have a legitimate business with the associated overhead and equipment or a shed behind his house with a Home Depot welder, a disc grinder and a tape measure that he can't use?

Not trying to bust your boys, just trying to illustrate some of the things you need to think about. Be honest with yourself (and the guy doing the work) about your budget and how far you expect it to take you. Building a car is great, but running out of money before it's half done can be demoralizing.