Well, I'm an artist, so its a little different... but if you were just financing the tour like in the OPs case, I don't really see the point of him going. Thats why I said hire a tour manager (Also, the tour manager is gonna be doing most of the driving).
So in a 8 person van, you have 1 tour manager, 1 dj (you only need one for the whole tour), and 6 slots to divy up between 3 acts. A headliner, a midcarder, and an opener.
The opener is just happy to be on tour. The midcarder is good with a nominal amount... I'd say for the 15k example, I would pay the midcard 3k and the headliner 6k that translates into $100 a show guarenteed for the mid and $200 guarenteed for the headliner. You can negotiate spots/venues for 6k (because they keep 100% of the bar and are given a flat fee to let the tour take the risk on collecting the door/ticket sales), then with travel and lodging you are looking at probly 20k in expenses (total) just estimating. The artists will make additional money by selling cds, shirts, etc, and you can also by having a tour cd or shirt with a track from each artist... something along those lines.
The artists, the venues, the hotels, the cars, all booked ahead of time before you leave on day one.
Before the tour even begins you can calculate the expenses and the projected return cause everything has set pricing.
The only thing that fluctuates is draw (fan turnout) so you can't book bums. But most artists that are about at the point where they are popping and people want to see them dont have 20k to tour themselves, so its not hard to get solid talent.