I don't consider any of the Palitoy carded figures to be particularly rare, they are just desirable especially the earlier ones with the logo on the front.
Just had a quick look on ebay, umm... yes very expensive with a 12 back Darth Vader AFA 90 £2,249.99 and a few others over the £1,000 mark
Each to their own I guess but Meccano, Harbert, Ledy and Glasslite carded figures are far far rarer and in my personal opinion much more desirable and worth the premium price.
Also I've noticed the price of trilogo's going up and up on certain figures - again a surge in popularity in this area.