At that price he's a deal. He'll probably get more. He's a better player than Hardy is IMO, although I like Hardy quite a lot too.
Justin Smith has never put up double digit sacks yet he was one of the best if not the best defensive players in the game for years. And he's still damn good.
It's possible he gets more. But given he's slightly older (will be 29 in November) and has had rotator cuff issues, I think teams will be hesitant to commit more than about $15-18 million in guaranteed money. Which is part of the beasis for my estimate.
I don't think Justin Smith is a great comparison. Smith is only one of 2 truly disruptive 3-4 DEs IMO (JJ Watt being the other one). Smith is about the bare minimum in size requirement (6'4" and 285) to be able to hold up against the run as a 5 technique. He does it because he's such a beast, has great strength (and quickness) and a high motor, I think Bennett is too light in the lower body to hold up as a 5. I think he's really best as a 7 (LDE in a 4-3).
I think Hardy is going to get paid more than the other DE candidates simply because of his age/mileage (and sack production). He's young and healthy. And teams pay looking forward, not back.