Registration fees not only vary from state to state, the basis the fees are calculated on vary. Some states charge based on the vehicles value, while others charge based on the weight. Here in NY for instance, any passenger vehicle (includes motorhomes) weighing 6951 lbs or more is charge $70 per year. California, on the other hand, uses a more complicated fee calculation than just the weight of the vehicle.
This link will take you to the California fee calculator pages. Indiana charges a flat $28.75 for a new motorhome registration, and $29.75 per year for renewals. That may seem low compared to NY perhaps, but then Indiana charges a yearly excise tax that NY doesn't. Any way, as you can see, without more details to work with, such as the RV size, weight, and value, there isn't a lot we can tell you.