Loremaster Legacy is on my wish list 
I did notice that there are a few herbalists scattered around the city, but would the prices (multiple gp) place their services out of the range of the average low towner?
I think it depends on what they need. Shop owners, skilled laborers, and some criminals could probably afford many of the herbs. The temple healing services are a different story, and are written in as a source of friction between one group of priestesses and their deity.
I think there are also a few ways to look at a game economy.
Bottom line for the players it's a reward system, so costs have to be set based on their enjoyment of game-play. Basic supplies have to be accessible, but you don't have to put every sundry they need in a storefront. The old Martial Arts Companion gave a really good suggestion for this. Martial Arts characters would learn new skills by joining a martial arts school; such a school would probably have tournaments, and would potentially have rivals. Accessing higher learning would require advancement in the school under the formal rules of the Martial Art.
Magic, and access to magical resources / training / items may have something similar. It's going to be more interesting to the players if there is personal story advancement as they build their character.
For the setting, an economy has to have the appearance of function, or in a dystopia the appearance of non-function. In a functional economy the shopkeepers have enough customers to make some degree of profit, and the average person has their own basic needs met. A cure for blindness might be out of reach for most, but a treatment for the symptoms of a cold might be accessible to many. The shopkeepers would have most of their needs met by the common people buying the inexpensive stuff, and the occasional major purchase by the well to do would be a bonus. The common folks don't need a set income, just come up with some rules for what they can and can't obtain at various class levels based on the feel you want for your settings Sel Kai. If you need the injustice of children routinely dying for lack of medicine, then the average person makes less than they need to get by.
Loremaster Legacy gives some good examples of shopkeepers, and patrons. It also has an example of the sort of people who may reside in Sel Kai for periods of time. Eidolin is sort of an Eden for the local nobles, and super rich. Sel Kai city has other nobles in Residence, and it's own rich.
It might be worth looking into how things worked during the golden period of a place like Venice or Bruges when deciding how you want to portray the background. In particular how people arranged apprenticeships might be useful, as would how people entered into the priesthood.
Magic shops need customers to survive like any other business, and won't exist in Sel Kai if they don't have patrons. You can of course add in a "Ye Olde Magic Shop" or two if you need one, or perhaps make such a service a part of another business. For example some of the dark temples might sell evil spell books or items if you have the right contacts, and if it serves their own goals to do so. Prices don't have to be coin, perhaps they want you to kidnap a child for tonight's sacrifice. A seer might have a selection of magic to sell to people, but only people his scrying shows to have a certain kind of destiny
