Can't help ya, haven't seen any deals on this recently. I know a while back Gamefly had some decent prices on the PS3 and 360 HD Collections, so I'd keep an eye on them to see if they put it on sale again (assuming you're OK with used).
I'm actually interested to see if these collections (specifically the 360 one) do become rare and hard to find over time. They got such a bad rap, I wouldn't be surprised to see these slowly creep up in value over the next year or so. I know Amazon hasn't had new copies of the 360 version for a while.