We took the number 1 yellow bus from Da Nang to Hoi An and back. We caught the bus at the cathedral on Tran Phu. On the way back we got off at the riverfront stop near the Han market. Cost was 20,000 per person each way. On the way there the money collector charged some tourists 30,000 each. There also was a group of 3 girls who disputed the charge he was demanding and they got kicked off the bus. We handed him 40,000, pointed to each of us. He didn't argue with us at all. On the way back there were no price discrepancies heard.
Easy way to get to Hoi An and back for $1 CAD
Thanks to everyone one who previously posted about this option