In my mind, the main difference is you’d be starting with an unknown quantity....... that could easily suck up another several hundred dollars worth of non-go fast parts...... all of which would have to come out of the budget.
That’s the intangible part of starting with nothing but a fixed number dollars.
I feel it’s a clear advantage to be starting with something you know.
Again....... not my rodeo.
You’ll do it your way.
