It has been a long time since I pulled a 5th wheel over the Alaska Hwy. the last 4 round trips have been in our truck camper. Last trip in 2011. We normally will average between 12,000 and 15,000 miles, depending on our route. So I will use about 1,100 gallons of diesel on the trip. We will normally spend about half our time boon docking (free) and the other half in private or government type campgrounds.
To budget my costs, I add up the major items, fuel, camping, entertainment , etc and I can have a great trip of about 100 nights for about $10,000. We eat out very seldom, don't often go to the paid tourist type entertainment events, etc. there are some costs I can control to some degree, such as camping costs and others are somewhat fixed, such as fuel.
It is much easier to find good boon docking spots in northern Canada and Alaska than in the lower 48. So we don't tend to stop a great deal, prior to the Canadian border. I go to Alaska to spend my time there, not setting in campgrounds along the way. How many days of travel to get there is a very personal matter. Some of our forum members, due to age, health or lack of, enjoyment of driving, etc, take take 3 or 4 times as long to get to Alaska than I tend to do. But after 13 round trips by RV, to/from Alaska, we know where we want to spend our time.