I think prices for these are unpredictable. They used to be higher but aren't so popular these days so you can pick up some great bargains even for rarer ones (when they are available that is)
I have a theory on that. The main few big collectors now HAVE all the ones that used to go for higher, and we have them in good condition. We were all collecting them at the same time and fighting against each other to win them. But now that we mostly have those horses we can settle back and watch them sell for way cheaper than what we paid. There also seem to be more popping up on ebay than there used to be. There was a while when I'd only see maybe 3 a year. Now there are regularly a few up.
There used to be another website on them that I liked for reference. That one seems to be totally gone now, but it had "rarity scale" from 1-5 on it ranking the horses with how hard it was to find them. It had a few EK horse photos that Wystearya doesn't have, and Wystearya has a few that that website didn't have. I wish both were still up because I liked to cross reference.