We just finished a two months tour of 8500 mile, 5500 of which were towing miles.
Stayed at a mix of state parks and private campgrounds throughout IL, MO, TX, NM, AZ, NV and UT. From the day we left home with the TT and TV loaded for the trip, our cost was $90.00 a day, that was total expenditures, gas and all.
There are only two of us and our dog, we pack our lunches or eat in the TT at a rest stop. We mostly hike or sightsee with the TV. The DW puts something's in the crock pot for supper when we get home.
If we go to a state park and stay, it is cheaper because we do not burn gas sightseeing.
Yor expenses may be more because of your kids.