Given that paidranks has a few bugs that need to be resolved as well as a lack of updating I have come up with my own version. Costly Ranks gives players the ability to buy their next rank according to how you set it. Includes multiplepath support.
Costly Ranks requres you have vault along with both an economy and permissions plugin.
Costlyranks.use
If you have any problems or suggestions feel free to ask for them.