I work backwards. If something is "common", then by its very definition, it's readily available. Maybe not in every household, but still available. From there, decide what types of things or services will fall into which levels of the economic strata to make the game world make sense.
For example, a +5 weapon seems like a common item, but IMO, requires a great deal of effort to produce. These could be purchased by guards and soldiers, but only if they save for quite a while, much like a decent-quality cavalry mount. Ta-da, there's your price reference.
Low level charms might be much more common, but would probably be focused in their abilities. Most of the spell lists and alchemy rules are about enchanting items for adventurers, who generally demand a higher quality, and a broader scope. So, IMO, you might consider that magic that is "common" might not necessarily be on an existing list, but would be of practical daily use to the working class. Imagine a charmed plate that kept itself at a constant 40 C temperature. Not a lot of use to most folks, other than as a comfortable bottom warmer. But to a baker, that's the ideal temperature for cultivating yeast and rising bread. Place a metal bowl on that plate, cover it with towels, and even in the cold of winter, you can raise bread dough without having to excessively heat your kitchen.
How much easier would a chandler's job be if he had the magical equivalent of a fan? Something to circulate air over the tapers as they come out of the wax, letting them set before the next dip. A wand of 10 kph air gust, in other words. Not very practical for an adventurer, but very handy for any number of industries - blacksmiths, tanners (fume dispersion), etc.
And if these items are targeted to the working class, they must be affordable BY the working class. They might be journeyman-level expenses, much like a set of good quality tools, a purchase that is only made every few years or so, but something that a working person could save for over time.
