I can't offer any advice on RV costs in Alaska...but no matter how you slice it, it's expensive.
If you want a cheap trip to Alaska without going to Joe's 1960's extremes, invest in the best tent and backpack you can find and fly up. Lots of places to camp during May - September, you can mix in a variety of B&B's and you can get a variety of scheduled/unscheduled transporation options and with the money you save from fuel and other travel costs, you can eat out quite a bit.
In all seriousness, there's many ways to shave a penny or two here & there that adds up to some noticable $$, but an RV trip to AK will be near $10,000.
While not going back quite as early as Joe, I remember at least one trip where my entire trip was circa $500; fuel, eating "out" at all times, the rotating stash of cash to keep $300 visible for the Canadian authorities, sleeping in the Jeep, AND a motel in Northway and Seattle....the fact that there was motel in Northway and the fact that the Seattle motel was $19.99 should date the trip.