First off: as I recall from the original session, I made it clear that you could buy Healing Potions for 50gp a shot. It seems only fair to give new players the same sort of options, especially when their character classes restrict the amount of actual money they can start with.
But to answer your actual question… you’re right.
I imagine that by the time you get to the upper spell levels the cost would increase exponentially, simply because most casters of that level would have better things to do with their time and because the demand would be so much greater.
Any temple with access to an alchemical lab and the right ingredients can put their acolytes to work scribing low level scrolls and enchanting potions. If they want to create something capable of 6th or 7th level magic… chances are that even their high priest won’t be up to the job and they’d need to find a higher level outsider.
Also… you’ll have a chance of failure when trying to cast spells from scrolls of a higher level than you’re normally allowed (DMG, p.196) . So even if Emmerus (at 4th level) did somehow get hold of a 7th level spell scroll (not normally castable until 14th level) he’d have a 50% chance of failure with a 35% chance that it rebounded on himself and his friends.
