$$$$$$$$$$$$$$ used to be reasonable back when I moved up there. Early 80's. Now, not so much. For a Class A RV Bellingham to Skagway or Haines. $3K, give or take, plus a cabin on the vessel and cafeteria style meals. The Columbia does have a dining room vs line style chow on most Alaska ferries. I've ridden the AMH system dozens of times and they have pissed me off more then left me pleased with their service. They are well trained in an emergency situation on or off the vessel. BUT, for what you are paying your rig should at least get a wash and wax detail while on board for the cost.
I won't go into all the bad experiences I've had on the AK state ferry system. And they don't even charge enough to cover expenses. The state legislature covers the gap with oil tax money. That's why there is no state sales tax.
I spent 25 years of my life in AK. Great state. BUT the ferry system is over priced and mismanaged IMHO. The workers are unionized and over the years have put the AMH system in a no win situation to serve the paying passengers it attempts to serve.
George