As high as the registration, taxes, and insurance costs for California might be, they will be small compared to the cost of the money you will have tied up in the motorhome: depreciation, interest if on a loan or lost income on the money tied up in it.
My $58,000 (used price) motorhome cost my about $8000 the first year, declining to about $3000 in the seventh year, with about $30,000 of the depreciation now behind me. Scale that to any purchase price. The parts you are worried about, insurance, fees, taxes are less than a third of the whole cost of ownership. That is still not including mileage-based operating costs like chassis maintenance, fuel, tires, which have averaged me about $0.40 per mile but creeping up with fuel and tire prices, and rising labor costs.
We tend to fret the nickles and dimes while spending the dollars. You've apparently gotten over the ownership cost hurdle with the fiver, just recognize that it will scale up with a higher cost with a higher value, and the nickel and dime parts you mention scale the same way, when you consider your present tow vehicle and RV as a combination.
