Nebulous
Legend
Those bad boys are from the last set, and Wizards decided to go with Very Rare as an extra kick in the butt with that set. The Hydra is one of the Very Rares. How rare are they? I hear you asking. I bought 20! Boxes of that set and got 3. 3 in 160 packs. The ratio of that fig to all the others is just absurdly low, as is all the VRs in that set. Ugh. On the plus side, it is a bad ass figure. I totally have mine, and it's really nice.
Zen
Yes, it IS nice, and I would love to have it. But I already have the green mini hydra and it has worked well. I don't like to collect those in the sense that one would collect trading cards (which I don't either), and i would totally love that heroslayer, but it's singular price is just not worth it. I have seen (and own) non-D&D miniatures, such as a Huge-based fire hydra, that i bought at a Michael's hobby shop for $10.
Edit: Lords of Madness was the last set I actually didn't get, except for a few singles. I wasn't gaming at the time and while I do think it was an excellent set, I couldn't justify spending hundreds for something that would literally sit in a box and collect dust. Still, I'd pick some up now if i could find a few well priced.
I don't know what anyone else thinks, but I got some of the last Pathfinder sets and the quality of the plastic wasn't nearly as sturdy as the DDM ones. I've had bases come off and plastic pegs crack and arms break. They feel weaker, but the DDM ones you could slam against the wall and they'd make their Con save and be fine!