If we're talking about UFA's available for cheap, we could do worse than Christian Ehrhoff, a smooth-skating left-shot defenceman who'd instantly upgrade our blueline.
He's the kind of defenceman that the Canadiens look for, what the managers were hoping for when they signed Tom Gilbert and then traded for Jeff Petry, a really agile, almost-elite skater who can break the puck out, either with a quick pass or by skating out of trouble. He's really brainy, almost Markov-lite in that sense, but certainly much more fleet of foot.
Paired with P.K. or Jeff Petry, he'd be a handful, pretty hard to get around, and always a threat to turn an opposition rush into a three-on-two going the other way. Let's say we keep P.K. and Andrei together, and have Christian Ehrhoff with Jeff Petry, that's four guys who can move the puck, and turn defence into offence in a hurry.
Or, if we want to ease up the minutes on Markie, we slide him down to the second pairing with Jeff Petry.
On the third pairing, you could have Alexei Emelin and/or Nathan Beaulieu with, on the right side, Nate, Greg Pateryn or Jarred Tinordi.
While the ticket price for Mr. Ehrhoff may be dropping daily, he'd probably come in at what he played for last season, $4M in Pittsburgh. Consider also that his buyout from the Sabres pays him almost a million dollars a year for the next decade. It shouldn't really enter the equation, but then again maybe he figures he'd like to play for a winner and adjusts his demands accordingly, if the thinks the Canadiens roster and recent performances give him that opportunity.
Practically, with Nate and Jarred needing waivers next season, and needing to be on the 23-man roster, it would require almost certainly that Alexei Emelin be traded away, to remove his cap hit, and unclog the defensive corps of too many bodies, to say nothing of Tom Gilbert. The kids need to play some, after all. Whether Alexei would waive his No Trade Clause, and whether the Canadiens think they can do without his physical presence is definitely in question though.
As a fan though, and having appreciated Christian Ehrhoff's turn as a Canuck, I would very much be down for an Andrei-P.K. and Ehrhoff-Petry Top 4, with the kids providing in my opinion a raft of good options for the third pairing.
Man, would we be skating with that defence corps. Other teams wouldn't know what hit them.