Changing rear ends but also driveshafts?

Now someone informed me that changing from a 7 1/4 rear end to an 8 3/4 means my drive shaft will no longer work and would need to be shortened and rebalanced or buy a new driveshaft.

Now I know there are no companies locally that can shorten and balance a driveshaft. So shipping one is going to cost me a good chunk of change.

At the same time so is buying one. But if I do buy one how do I know which one to buy?