In the vanilla game, the cost is always 10 gold, despite what price is shown in the Travel menu. (only 10 gold is removed from your inventory, even if it says the trip will cost more)
The MW Code Patch fixes that glitch, so that you pay the amount shown.
But anyways...
In both cases, the NPC's Disposition determines the cost amount in the Travel menu. The more they dislike you, the higher the cost.