what is the rarest cp i can buy?
Tuberous sundews, edwardsiana on the black market, stuff like that. There are rarer plants but they are not for sale, just trade from generous growers.
The cross between a butterwort and a VFT is rare. It eass dentists. has a potty mouth, and is constantly hungry.
Tuberous Sundews, VFT "Gold Strike", Cobra Lily, perhaps D. madagascariensis or D. graomogolensis, but finding those is... really difficult.
Tuberous Sundews are hard to grow, I would not make them a beginner's plant. Gold Strike grows like any other Venus Flytrap but the specific cultivar is somewhat rare.
Cobra Lily is legendarily hard to grow, again, not a beginner's plant.
D. madagascariensis appears on ebay every so often, and is rather neat, apparently it's more akin to a climbing vine than a typical Sundew.
D. graomogolensis is by far the most beautiful sundew I've ever seen, but good luck finding it.
Now, onto a slightly different topic, if you're looking for very unique CP to buy, there are several less rare CPs that are still really interesting.
Yucca Do 1713 is a butterwort that is pretty easily obtained but is a true mystery -- no one knows what type of Butterwort it is, it was found in the Mexican wilderness and unfortunately no log exists.
D. Filiformis "Florida All Red" or D. Filiformis Tracyi are interesting sundews that grow like blades of grass -- like 3 foot tall blades of grass, mind you.
Pygmy Sundews are interesting little plants, too, if you don't mind'm small.
Several varieties of VFT are interesting -- fro the big (B52 for example) to the weirdly colored (Gold Strike, Red Pirahna), to the mutated (Cup Traps).
I don't see many Parrot Pitcher Plants in cultivation, that might be interesting to grow.
I don't know if this qualifies as "rare," but I've been trying to get my hands on a Drosophyllum (dewy pine) for months. I've never seen it listed on eBay. A few CP seller sites have it listed, but all are "out of stock" or "in propagation." Frustrating.
Have you tried looking for Drosophyllum seed on the various carnivorous plant seed banks? Both the CPS and the VCPS currently list it on their website (along with many of the tuberous Drosera that people seem to be having a hard time finding). I suspect other seed banks closer to home will also stock it.
Cory: I have indeed found the listing at the CPS website. I think I'd have to be a member to get some from there. So maybe I should stop being a cheapskate and join the club!
Even if the only value you see in joining a CP society is in having access to their seed bank, the cost of joining is usually offset by the low cost of the seed. If you're comparing the seed prices on eBay, you'd only need to buy a few packets of seed from the society to break even.
Sarracenia Northwest (www.cobraplant.com) has a couple rarities, for example N. hamata, Heliamphora minor, some Utricularia i think, and Cephalotus. Beware of N. hamata, though, it's priced at $165!