Nearly 500 miles in 49 days, about 10 miles a day. Actually pretty average through NH and Maine. You seriously work for your miles up here. There might have been a few zero and near zero (NEARO) days in there too, which reduces the average. This section is arguably the most expensive section to hike.
But yes, the slower the hike, the greater the costs. If you can do the hike in 90 days as opposed to 180 days, there is a significant savings. But probably not by half. Towns are money pits. If your not careful, you can spend a lot of money before you realize exactly how much, especially early on when you think you have plenty and the weather sucks.