I would think that hydrocarbon fuel costs would vary widely from world to world, and even from country to country on that world (if its not an unified planetary government)
This would depend on many things, such as resource availability, tech level, commonality of hydrocarbon use, fuel taxes, etc.
Hydrocarbon fuel would be cheap on worlds which are rich in life, have large petroleum reserves, are low enough tech that hydrocarbon fuels are used commonly and there is a big hydrocarbon industry, and where the local goverment doesn't tax the hell out of fuels.
Hydrocarbon fuel would be much more expensive on lifeless worlds or worlds which have been recently seeded or terraformed, since there would be no oilfields built up from billions of years of life.
On very low tech worlds, there may be no practice of refining hydrocarbon fuels.
On high tech worlds, it may be hard to even find hydrocarbon fuels in any decent amounts. There certainly wouldn't be gasoline filling stations on every block. There is more likely to be self-service charging stations for fuel cells, micro-fusion plants and batteries. (gas or liquid hydrogen or straight electricity).
High tech worlds with large oil reserves will likely refine oil for industrial uses (synthetic rubber, plastics, industrial lubricants, oil based chemicals for manufacturing or scientific use.) It should be possible to purchase hydrocarbon fuels on these worlds from refineries or industrial chemical companies, but there still wouldn't be gas stations around.
Worlds with strict pollution laws may even outlaw hydrocarbon burning engines.
Just my thoughts...