When we started full timing we lived in NH and the plates for our new 2004 motor home and car combined was close to $2000 - most of it being the motor home.
We decided to change our domicile to a more reasonable place. We had lived in CO before moving to NH so checked to see what plates/tax would cost us - it was about as high as NH! So we moved to SD - $186 combined - car and motor home.
Ten years later, after we bought a home in CO and licensed the motor home it was a lot cheaper - a couple of hundred dollars as I recall - because of the age and current value I guess.