That was my first thought.

In either case, I would get the maps unless you can memorize or otherwise plot the route some other way. Also, the maps can often pay for themselves by identifying free/cheap camping. For example, if camping is shown in a city park, it's likely going to be free. If there is camping at a fairgrounds, it could be free or cost a nominal amount like $5. U.S.F.S. campgrounds and state parks are generally (but not always) cheaper than private campgrounds. The type of campground will be described on the maps.

I have done all of the NT once, the western portion between Bay View, WA and Glacier N.P. a second time and the section between White Fish, MT and Eureka a few years ago. Once you tell us which direction you are considering, maybe we can give you some additional insight.