I had some help and made a mod that raised the prices as follows:

Towns without a stable:200 gold

Towns with a stable:100 gold

Ive been trying to get help to make it so the price is based on the length of your trip and Hearthfire Houses destinations are added once they are built.

This just alters vanilla carriages not hearthfire carriages.

If anyone is interested drop me an email addy or pm with your email addy and il send it to you....i dont recall how to upload this anywhere so il do it old school.

If anyone wants to help me with the future updates get a hold of me and il see to it credit is given.

Credit:

Docblacky - step by step walkthrew

Qwert - Manual work