The Miami Herald suggests free agent Brian Hartline would be willing to accept a three-year deal averaging $6 million annually, or "maybe less."
Three years would take Hartline through his age-29 season, allowing him to reenter the free agent market at 30. It'd make sense for the player. $6 million annually is also a reasonable cost for a receiver lacking a high ceiling, but possessing a solid "floor." The Dolphins are more than capable of paying it.