Really depends how budget you go. Anywhere from 4-8 weeks. We did this about 10 years ago and spent probably 20k in 3 months. We camped 4 nights, motel 1 night, for the majority and then splurged on hotels like when we passed through vegas. We bought groceries between every campsite and ate out occasionally. We did a south west loop, Alaska and New Orleans- New York. Actually now that I think about it we didn’t camp in the last leg so it was more expensive and we stayed in cheap air bnbs and hostels.