Buying my first Grizzly… maybe??

I am looking into buying my first Grizzly. I have talked to an individual that has one on the market. He said that the high gear will need to be rebuilt. It runs and goes in low gear, but it will not move in high. As I am not very familiar with the Grizzly, how much would this cost at a dealership and/or is it something I could do myself? Any input would be greatly appreciated. Thank you!