Okay, where can you easily get a guy capable of giving you 20 ES goals a season somewhere else for cheaper? You're grossly underrating Sheary, he's a solid 3rd line offensive player who can chip in anywhere between 20-25 goals and 35-45 points over a full season.
First the pens have so much skill no team is going to expect those numbers on their team. In general though small scoring 3rd liners just have never held much value, especially when they are overpaid for what they are like Sheary.
18 goals and 12 assists isn't really anything special, those are depth player numbers and usually depth guys can fill other rolls such as PK or add a physicality element. He also has a very high SH%.
He's with guys like Byron, Wood, Perlini, B Mcginn, Nieto, Lewis, Helm, etc. except a bunch of those guys have a better all around game.
If you want more depth you can get guys for cheap in UFA, or give that ice time to a up and coming prospect. I definitely get why Pit would want to move him but I don't see what team out there would want him, let along give up anything of value for him.