I say 5yrs at 11-12M per year, about what you said.
Long shot, but if the Celtics were to make an attempt to get Monroe, they could use TPE (10.3M first year) and send a few picks over to Detroit. Detroit made it clear they wouldn't mind letting Monroe go as they already have Drummond, Stuckey and Smith. Still, that's a long shot.
Greg Monroe earned 3M last year.