Sure you can hire a motorbike in Hoi An and scoot around (we did, from the man across the street from our hotel for 120000 VND, thats about $6 USD ) and that was fine, despite the fact that the Vietnamese aren't very keen on a map or a road sign we managed quite easily to get ourselves to My Son. Of course our hotel pushed for us to take an organized bus trip (yuck) telling us that "it was much easier" and it was "quite a long way to go", after much traveling in S.E. Asia I have learned that "quite a long way" can be as close as a kilometer or up to 100km, My Son was 55km out of Hoi An, hardly an epic trip! We got there just before all the big buses started to arrive and enjoyed walking through the ruins in relative peace and quiet. Then having saved $ on that we decided to hook up with Hoi An Motorbike Adventures to take us a little further afield, and we are glad that we did, they took us on trails we never would have found (again with the lack of maps and signs) with great local knowledge we had a fantastic day!! We took the "Higher Than Hai Van Pass" trip, and it was brilliant. It was so nice to see Vietnamese people smiling, waving and going about their business without ever trying to sell you anything, cruising through tiny lanes around the villages and rice paddies and avoiding the highways where ever possible. We went with Simone (an owner of the company) and a mechanic, lunch, drinks (not alcohol) wet weather gear and entrance fees were all covered by the cost, and it was very reasonable. We went up through the mountains and along the coast, visiting many local sites, including Monkey Mountain and Marble Mountain. So sure you can hire a bike for bugger all but if you want to get out and about and off the well beaten tourist track I recommend you look these guys up, they were awesome and Hoi An is a beautiful little town to spend a few days (we came in the off season, a little rain beats the hell out of a million tourists anyday) and it was reasonably quiet and peaceful.