Its just the fact that you don't see these figures much at all, as mentioned, the last ugnaught sold for £1440 back in 2015, but from memory it wasn't in the best condition, I was half joking with the valuation on the Ugnaught, but nothing would surprise me in this game, I've never seen one come up, the one I got was from a collection, realistically, if you wanted an 80 grade or above you must be looking at £5k due to the rarity of the piece.
As for the Yoda, I have actually seen more of these for sale than an Ugnaught, being an iconic figure does help with price and a good example would certainly demand £8k upwards.
One of the easier Palitoy 30 backs was Lobot, but I cant remember the last time a good condition example came up for sale, I'm sure someone will remind me, I think the only way you can acquire these rare figures is by buying a full collection, the other possibility would be a situation that occurred a couple of years ago at Vectis, with Mr Carpenter, but this in my opinion was a one-off, he will certainly have been able to afford a top drawer bathroom, which was his Son's reason for selling.
I think for us collectors wanting to complete our 30 back runs its a matter of being very very patient....and I mean years of patience!!!