I have to correct you on a couple of things
Certain animals are so closed when it comes to genetics that they might have offsprings;It doesnt necesarily make them of the same species.I give you an example......A mule is the product of a dunkey and a horse,and we all know the parents are two different species.Same goes with a patty and a swortail,they might even look alike and capable of producing babies but,the reality is they are different species.This is what we commonly call a hybrid.
A mule is not viable offspring though. Mules are created when horses and donkeys are mated and their offspring (the mule) is a combination of the two species but CAN NOT reproduce. All mules are born from coupling horse and donkey. Some fish can be crossbred and will have offspring that are like mules (by which I mean that they are sterile). In the case of platies and swordtails, they can be bred and their offspring are able to reproduce. This indicates that they are actually the same species but swordtails have developed differently probably due to isolation from platies in the wild. Its like different "races" of people, caucasian, african, or asian or even pigmies are all members of the same species but look very different.
I looked up a little on endlers and read that the place where they were originally found was destroyed. The article said that was the only confirmed place that they have been found though there have been claims from other areas of Venzuala. That would probably be why they are so expensive. I will have to see if there are any good breeders near me. Though I kind of doubt it I live pretty far from any major cities.