I would say $5K min realistically. This will allow you to get started (hotel cost, food, supplies etc..), pay the bills and have some left for any problems. Figure three months to get up to speed to build some reserve. Of course this is outside the expenses like truck payment, insurance etc.., that I would have three months saved up so not to worry about it.
I can tell you you can do it for a lot less, maybe near to nothing but I don't recommend that at all.
Hope that helps.