Be prepared to have a worn out truck, so you have got to justify that cost. You need more than enough to make the payment and ins ( if you have a payment) Its a hard thing to put a price on, but some guys have some good advise
The way I do things, is I furnish a truck to go back and forth to work, etc. My thinking is, if I have to pay someone to drive their truck, I would be better off to go buy a truck and let this money make the payment, plus its a tax deduction (the payment) I did at one time pay one of my guys $50 a week plus fuel, but that $200+ a Month, I was paying him and getting nothing. I had to buy him tires (he paid me back, after a while, BUT) I went and bought a 2001 Ford F150, for $2500 and paid myself back each week and then I had a paid for truck, for the workers to drive
This may not help, but dont use your truck for nothing, make him go buy one, for you to use
Good Luck