One name (actually two) immediately comes to mind. The second name is Tim Moltzen, though he wouldn't really be classified as a marquee player.
Anyways, the name I was first thinking of would be Chris Heighington. Likewise with Moltzen, Heighington was apart of Central Coast Rugby League growing up. He would be a great player for marketing (in Central Coast) for that reason, along with his awesome personality. He rarely gets injured, and gives 120% every game, and does the hard yards when the team needs it most. He can lead a pack of forwards any day of the week and twice on Saturday. The only real con is that he is not wearing a number 7 or number 1 (which are probably more "sell-able" jersey numbers).
At the end of the day, he would be my choice as a "marquee player" for the Bears. I'm not sure how much money the Bears have, so Chris shouldn't set them back as much as Thurston or Hayne (even though he is better than them lol). But yeah, Heighington is ours and the Bears aren't getting him :D