I'm involved in logistical support for a race team that races 2 Trophy Trucks in SCORE and depending on the race we will have anywhere from 10 to 50 crew members. Here is a pic of part of the Oshkosh team in action I did the logistics for in the 2010 Baja 1000.
There were 15 people involved in this pit, Oshkosh had 2 vehicles entered and we had 80 people and 23 support vehicles.
What you could spend totally depends on how much you are willing to spend on your support, that is, how much support do you want to have? How many people on your crew? Single support vehicle or multiple? What are you going to use for a support vehicle? You going to build the support vehicle yourself? In South America when the bivvy is close to a town, many teams put at least some of the crew in addition to entrants up in hotels. Are you going to sleep on the ground in tents every night? How soon before the race are you going, how long is everyone going to stay after? What amount of spares? How many wheels?
If I were you, I would put into your budget paying for a seat in a support vehicle and be part of the race the year before you plan to race so you can see what & how others are doing it.