Well, as I have been mentioned several times I guess i should contribute.
I think in terms of rarity Jason's site is a good guide, though with certain limitations.
It does let us know what could exist as packaging at least has been found. So if you want to know what figures are really hard to find, then I'd say the ones that have no record are the hardest. Of course the problem here is that it is possible they don't exist at all, so until one turns up it is kind of hard to say they are rare. Rarity implies few (though I'm not going to get into a long discussion about that word again...see other thread) In other words they are known to exist but you will hardly ever see one.
What does/doesn't exist is limited to the information at hand, given by those willing/able to share it. A good thing about Jason's site it that it is a living documentation, in other words he constantly updates it as new information comes in.
The Leia Bespin which I recently received, though full credit for its discovery must go to Lee Gregory, is a good case in point. Until the other week, its existence was not known to the wider public and Jason's site was the first place I looked to double check. I was fairly sure I had never seen one, but the site confirmed that packaging had never been seen. So currently this is the only widely known one that exists, which actually makes it one of the rarest figures I now own. There aren't many figures in my collection for which I can say it is the only one I know of. But I doubt that status will last for ever. Others will always be discovered.
Does it make it mega expensive though? To be honest, not really. As Spoons said, these cardbacks don't really go for much, despite the rarity of some. I think the most I ever paid was around £450ish for a Yoda. But a mega popular character and I can't recall ever seeing another one come up for sale, so was a major bidding war on eBay.
For me the rare ones on Jason's site are the ones for which there is a cardback, but no known MOC. Sadly the site at the moment doesn't tell us that. And I think some of the evidence on there is anecdotal rather than actual. But is is defintely the best source of information and the place anyone should go to first! 8)
So in answer to the original questions;
Values are all over the place, though I'd say up to over the 3k mark on some. e.g. 30 back Fett?
Some are definitely rarer than others, though this doesn't always equate to value.
Ones with the logo tend to be the more popular, with the 30 backs still holding position as the most sort after.
There are several lists on this site regarding rarity orders, though they change frequently as new ones turn up.
If you could be more specific as to what you are wanting to achieve with Palitoy ESB's we could almost certainly give you more accurate info.