I couldn't say if it's easy to get a long distance driver on short notice, as I booked mine weeks in advance. The drive between Hue and Hoi An is, if I recall, a bit less than 3 hours of straight driving. My driver waited for me when I spent perhaps a little over an hour exploring the Cham museum in Danang, but that was my only stop in Danang. Basically, I had him for a half a day.and a roughly 190-200 km drive.
You could probably get a taxi or a driver from Hoi An to Danang airport easily through your hotel, if not just flagging one down.