I don't know if the "unskilled labor" idea is solid, though; men of the paying persuasion are normally wiling to pay a good bit for even medicore service in this department. I think this field benefits from a bit more "charge what the market will bear" strategy, and that involves either arbitrally setting the going rate for service in a specific city, or feeling out the PCs to see what exactly they're willing to pay. Also, consider the range of services available on today's market, and the prices for those services -- in the essence of good taste, if you want to get an idea and have access to HBO, they do an a series American Undercover shows that follow hookers, which would give you a good idea of what the going rate is for specific services. After you have a good idea, remember that the situation is slightly different from that of a common prostitute -- so increase the price accordingly. If precautions are taken for the health of priestesses, then increase the price accordingly. If birth control/freedom from "worry" are guaranateed by the church, increase the price accordingly. You pay for quality, and if these measures are being employed, then clients should expect to pay well.
As for the a demarcation of prices... I agree that the high priestess should be separate, available only to rich merchants, wealthy nobles, and royalty. I'd figure that even novices would cost at least as much as a night's stay at an inn with a private room (2 gp), and possibly considerably more depending on the services rendered and the precautions the church provides.