I think 75 dollars a day would be a good estimate.
A lot of days, you will be well under that, but it would
give you a surplus for any of lifes little emergencies.
If it works out, your trip might be a little longer.
If the weather goes bad or you have major bike issues
it may not last long. Mostly luck of draw, and if the
highways gods smile on your trip.
Since I like a HOT shower in the morning,
I look towards campgrounds with showers.
I normally budget closer to 100 dollars a day.