The morphs or cross breeds are rare because not alot of breeders do it. I know kammerflage kreations sells them. As far as pricing you mean by breeder? I suppose some prices are just higher than others.
Different locales can be higher priced than others because they may be more difficult to get. Some of them are not imported very often and there isn't a big captive collection to work with. Ambilobes are well established but the mitsios or ankaramys aren't found very often. Color has a lot to do with it too. The very brightly or unusual colored pure chams can be more expensive because people want the jewels of the species. When you go get a dog do you chose the puppy that just looks alright and skip the one that looks like it could be in a show ring? No you probably want the pretty one! So that breeder can charge a little extra for that one since you and probably others really want it. Same idea.
The morphs/hybrids are generally lower priced because no one wants them for their breeding lines since they aren't genetically pure.