As far as the price added for being a het, that depends entirely on the morphs involved. For example, Hypos have come down in price quite a bit, so a morph that is het Hypo may not be that much more than one that is not. On the other hand, Desert Ghost is still a very high end morph, so anything that is het Desert Ghost will be pricey, and that price is justified. Animals that are het for more than one gene are also worth more. For example, het Albinos and het Pieds are both pretty affordable, but a snake that is het for both genes is worth quite a bit more because it has the potential to produce a Pied Albino.