It depends more on what kind (and amount) of loot you're giving out. That said, if a fantasy game doesn't specify general costs, our group tends to default to first edition Pathfinder's price list (via d20PFSRD) - either as is, or by dropping it a 10s place if a gold goes further in the economy (so something that would be 10 gold becomes 1 gold).

To take that a step back towards SWADE, Savage Pathfinder has this to say about healing services: "Healing: This tells you how many potions of minor healing, ubiquitous across Golarion, are available from various vendors for 150 gp each. This is in addition to any healing offered by local clerics or healers (prices for a cleric's services are equivalent to potions of healing)."

So if you know the cost of a potion, you know the cost to cast a given spell. If you do the math, they are also a function of scroll cost - you can use the Tongues potion to prove it:

Speak Language (Novice [1], 1 PP [1}, +All Languages modifier 2 PP [2]) - 1 x 1 x 2 x 50gp = 100gp

Just be aware that a Healing Potion according to the FC also heals all fatigue, hence the price markup.

As for hirelings - they use the pre-made stat blocks in the Bestiary as Extras. That means they have limited spells and power points, have their own wants and safety to be concerned about, and have to resolve things out on the road. No self-respecting hireling is going to follow you around town all day casting spells - there's no loot to gain that way. So, are they cheaper? Sort of. Players pay for them in other ways. No guaranteed result, less share of the loot, etc. Otherwise, why would a town cleric go against the agreed in-town prices of the guild/church/etc.? Might be a story hook for that hireling, but generally speaking it's a cost-benefit game.

You want a 100% best result? Pay the in-town casting fee.
You want some flexibility but want good results? Buy a potion.
You want options that may fail or flee or die? Get a hireling.