From the I-78 bridge website, it looks like the toll will be $6.50 if it's just a two axle MH. If you are flat towing a car, the toll will be $16 ($4 per axle). It's cheaper to unhook on the NJ side, drive the car over for $1 and the MH over separately for $6.50.
There is a free bridge that goes from Phillipsburg, NJ to Easton, PA but it's a tight ride through city streets on both sides of the river.
Tom and Katharine
'07 Winnebago Tour 40TD, 400hp Cummins
RVing for 19 years & 150,000+ miles