In case you haven’t heard, Al Horford just inked a five-year contract extension that will net him $60 million. The deal is the same length and amount as Joakim Noah’s, signed before the season began.

Normally Horford’s extension wouldn’t be mentioned here, but it’s part of a developing market that will shape Kendrick Perkins’s contract in the offseason. Let’s take a look at how big men comparable (or not-so-comparable) to Perk have gotten paid in the past year:

• Brendan Haywood – Six years, $55 million. In a word, robbery. In another word, stupid. In a few more words, Haywood is averaging 4.0 points, 4.3 rebounds and 22.3 minutes per game. Not a great return on investment, so far at least.
• Darko Milicic – Four years, $20 million. Manna from heaven, my ass.
• Horford – Five years, $60 million. A fair deal for the undeserved All-Star.
• Noah – Five years, $60 million. I love Noah’s game. His effort and underrated skill are definitely worth $60 million, if you ask me.
• Brad Miller – Three years, $15 million. Is it just me, or is it tough to justify giving $5 million a year to a 34-year old backup center who can barely move?
• Joel Anthony – Five years, $18 million. In other words, overpaid.

The market has been set, and — barring any huge CBA changes, which could certainly happen but are also unpredictable — Perk should be looking at something in the vicinity of Haywood money. (Cue Ron Browz: “We getting Haywood money! We getting Haywood money!” And… moving on.)

If Perkins does command such a big contract, should the Celtics be willing to pay it?

On first glance, the answer seems like an easy yes. Perk is one of the game’s best low-post defenders. He’s 25 years old. He has improved every year. He’s tough, and he’s rugged, and he’s had a lot to do with the Celtics’ winning ways the past few years. He’s kryptonite, for fuck’s sake!

But the Celtics are freeing money for a spending spree in 2012 or beyond. Signing Perk to a big contract could keep them from being big players in the free agency market once the Big Three Era finishes. The C’s will be rebuilding around Rajon Rondo, but they’ll need scorers to surround him with.  Dishing out a big contract to Perkins might not be the best way to spend their money.

Why not? They’ll also need a center to rebuild around, right?

But they already have Jermaine O’Neal and Shaquille O’Neal signed for next season, and also Semih Erden. Erden looked good in the preseason and has impressed Doc Rivers. Rivers even said, “He’s going to be a good big in this league and he’s going to be a good big in this league for a long time.”

If Erden can prove himself a keeper (and yes, I know it seems like a big stretch for a player who has registered three DNP-CDs in his first three games), he could make Perkins expendable. Think about it: all the things Perk is known for (rebounding, blocking shots, yada yada yada) are the same areas in which Erden should excel. And one has to believe Erden would come a lot cheaper.

I’m not at all saying the Celtics should let Perk go without a thought. I’m not at all saying, “Semih Erden is better than Kendrick Perkins!” Not even a little bit. I understand Perk’s worth as well as anybody. But if Perkins’s contract demands start to get too high…

I guess what I’m trying to say is this:

If you think re-signing Perk is an automatic, you might be wrong.