I think that you would need to make your own race. It's actually impossible, even using the Advanced Race Guide playtest rules; they don't have any way to give a race "constrict". However, I think that it would be reasonable to take it for no more than 2 RP, since it only takes 1 RP to get "bite" or "natural attack" (which includes gore, hoof, slam, talons, and wings).
You need to be honest with your DM, though: you're not making a standard race. Although it conforms to the standard 10 RP, it has abilities that are at least advanced (such as Fast), if not monstrous (such as Constrict and Can't Be Tripped).
So. Here we go! I found your query interesting enough to make a race, kind of based on Kin in the webcomic Goblins: Life Through Their Eyes. It's a man-sized snake, but with arms. If your DM is hesitant about allowing Constrict, just point out that it would only take the same +2 RP to add +2 to your armor (with Improved Natural Armor).
Degenerate Yuan-Ti
Like normal Yuan-Ti, this is a man-sized snake with arms and a human face -- but dumber. Yuan-Ti are normally geniuses, but these guys are like their Neanderthals: good at primitive tasks, not so good at advanced ones.
Monstrous humanoid (2 RP): You're a snake-man with a tail instead of legs. You have darkvision 60 ft.; but you breathe, eat, and sleep, just like anyone else.
Medium (0 RP): You're man-sized.
Standard modifiers (0 RP): +2 Dex, +2 Wis, -2 Int. You're naturally agile and tuned in to the cues of the natural world, but not exactly well-read.
Standard language array (1 RP): You start knowing Common and Aklo, since you're a monster. Degenerate Yuan-Ti with high intelligence scores can choose from the following: Draconic, Elven, Giant, Gnome, Goblin, Orc, and Sylvan.
Natural armor (2 RP): You've got scales! You gain a +1 natural armor bonus.
Can't Be Tripped (2 RP): You don't even have legs. How the eff is anyone ever going to trip you?! Whatever, they didn't put "can't be tripped" in the playtest; but for 1 RP, Stability would give a +4 racial bonus to CMD when resisting a bull rush or trip attempt while grounded. I think it's a fair price.
Fast (1 RP): You slither so well, you can catch almost anything. +10 to land speed.
Constrict (2 RP): You have an incredibly muscular tail. You can't use it to hold things like a Vanara, but crushing someone to death? Yeah. You can do that.
Total of 10 RP.
It ain't quick, but wild shape gets you constrict eventually.
Forget monk and just play a synthesist summoner with the right evolutions? I think they get constrict as an evolution...
Yes, and the original poster said that it was over-powered. Which is why I tried to give him something balanced. Whether I succeeded is another question entirely...
Huh, I didn't notice his edit.
I'd still do the Synthesist. Just pick serpentine, it's possibly the worst base form there is, do the constrict thing, and maybe make a bunch of suboptimal choices on feats or spell spell selection until you feel like you've sandbagged it enough to a point you're comfortable with the power level. It's easier to self-nerf a summoner down to a weaker level and still retain the ability to contribute to the party than it is to try and optimize a monk up to a point where he has the ability to contribute to the party. Plus if you go the power down route, you have the freedom to pick stuff purely based on what's "in character" without having to worry about being mechanically awful. Cause seriously, it would take intentional, conscious effort to mess up a summoner that badly. :)