Libya is not a particularly expensive country to visit. I was there for a week (last week) and stayed at the second best hotel in Tripoli (an international business hotel) for about €40 a night. Food is not expensive, and gasoline (petrol) is ridiculously cheap - about €1 for TWENTY liters, in other words, about .05 Euro per liter. Bottled water is far more expensive than gasoline.
By way of comparison, Libya is generally less expensive overall than Kenya, for equivalent food and shelter.
The economy is rather informal (although remarkably well developed) - if you discuss matters with the guide you initially make contact with, he or she can likely pass you off onto a 'junior' guide who will ride with you in your vehicle for much less money that the full price of a highly experienced guide who will supply their own vehicle.