How the cost permissions work:
1. Permission node must start with "permissionportals"
2. The second part of the node must be one of the portals' names, or "pushback" for the pushback setting (netherportal,endportal,pushback)
3. The third part will be the price you want a portal type to cost. (PUSHBACK DOES NOT REQUIRE A VALUE)
Note* the plugin will automatically pick the lowest cost permission set for each player.

Example #1: Player should get pushed back when trying to enter portal and getting denied. Permission to add: permissionportals.pushback

Example #2: Player should be charged $10 to use end portal. Permission to add: permissionportals.endportal.10

Example #3: Player should be charged $5 to use nether portal. Permission to add: permissionportals.netherportal.5