Well there are ways to build up your pay check (i.e. coming in on your days off), but I do know a lot of guys that need a second job to get by, but thats the life of a CFI.
I agree Nashua is very expensive, but its a nice place to live (voted best place to live in America, twice, by Money Magazine)...if you choose to live in the ghetto section of town, you can find rent that is a relatively lower, but still more expensive than average.