There are several systems covering maintenance. For RPG purposes, the most detailed and if you want to play a mercenary accountant, refer to the Field Manual Mercenaries.
Maintenance depends on what system you use. In Interstellar Operations, it costs 0.1% per ton of Mech in generic spare parts at a cost of 10,000 C-bills per ton of spare parts. That means a 100 ton Mech costs 1,000 C-bills per month. It would also cost the salaries of 1 Tech and 6 AsTechs to maintain totaling 3,200 C-bills per month. So in total 4,200 C-bills per month for a 100 ton Mech.
In Field Manual Mercenaries, it is a weekly maintenance cost of 75 C-bills flat per Mech. However maintenance is tracked by effective man-hours, with a 100 ton Mech needing 40 + tonnage/5, or 60 man-hours per week of maintenance. However under these rules, 1 Tech needs 1 AsTech as assistant to perform at maximum efficiency, else they lose 15% productivity if working solo. Together the 2 would generate 60 man-hours per week between them, just enough to maintain the 100 ton Mech, and their salaries would be 1,200 C-bills per month. So under these rules, that Mech will cost 1,500 C-bills per month. Why this divergence? Because newer rules track by Tech teams (composed of 1 Tech and 6 AsTechs) and 1 Mech needs 1 team, whereas the older rules used man-hours, and the number of man-hours produced depended on the skill level. Note I just covered technical maintenance. Administrative maintenance costs and medical maintenance for the personnel are tracked separately and would push up costs.
The rates for chartering ships is given also in Field Manual Mercenaries. The cost varies by the type of DropShip, ranging from 30,000 for a Fury to 8,400,00 for a Behemoth. Then there is the cost for the actual Jumpship at a cost of 30,000 to 50,000 C-bills per DropShip per jump.
Fuel costs for a DropShip are spread between Interstellar Operations and Strategic Operations. The first gives peacetime consumption for a DropShip at 15 burn days per month. So first you need to calculate out how many tons of hydrogen fuel is a burn day for your DropShip, then it is a cost of 15,000 C-bills per ton if you are buying and delivering to a forward base (costs vary if at peace, and hydrogen can be as low as 500/ton). However, it says hydrogen fuel can also be manufactured (via water hydrolysis) by any unit with a fusion engine, at a rate of 10 tons per 8 working hours.