Ok, what about peasants?
Let us posit a village of 100 people. 80 are income earners - the others are too young/old/sick to help. The average salary of a poor person (based on the income table) is 2 sp/day. I'm going to pausit that 60 people are poor (2 sp/day), and 20 are doing ok (the village is on a crossroad so there is a bit of trade) at 1 gp/day.
Accidents happen in medieval life - accidents where fast magical healing could save a life, or at least prevent an injury from being crippling or getting infected. I have no doubt that a potion of healing for emergencies would be greatly welcomed.
The 20 wealthier individual know this. and they form a pact to each save 1 sp/day. They are now saving 2 gp a day. In 25 days, this humble village can save enough money to purchase one healing potion.
So... it's not that crazy a price for magical healing anyone can use.
That all assumes a strictly medieval setting. D&D is not strictly medieval - it has wizards, clerics, and all kinds of magic creatures and things.
When I started this thread, I was just thinking about how 50 GP is a lot, especially for a 1st level character and given the relatively little healing involved. A goblin hits you with an axe and it takes a 50 GP item to heal it?
But then after a few posts and thinking about it some more, I realized--or remembered--that every setting is (potentially) different, and it really depends upon what the DM (as world-builder) is going for. As I said above, I imagine my own setting as being more akin to a magic-infused, animistic world akin to the way that ancient peoples saw the world, not the orthodox historical view of the medieval with some magic slapped on that that default D&D assumes. My issue with that is along the lines of what
@BlivetWidget said above, that magic is assumed to be rare but presented as common.
There's no right or true way to do it, except I think it erroneous to assume that all worlds must follow the same template and the same assumptions or go along with the default view. We can play with this and follow through with some kind of thought out internal consistency (aka, the infamous verisimilitude).
So in my world, in the village that you describe, there is an herbalist who lives on the edge of town, who is deeply connected with the living (and magical) world and creates herbal concoctions that are available to villagers, in the same way that there's a smithy or a tavern or a shrine. Druids and rangers know the intrinsic properties of the living things of their region, and can find plants or springs that can heal or provide visions. Priests can bless water to offer for true believers. And so on.