Thanks for the kind words! Short answer - no, the price is hardcoded.
I did that on purpose. Potion pricing is heavily tied to the market, which changes value every day. If prices were adjustable, players could just buy potions cheap whenever the market's low, then dump them on characters for a big profit once demand spikes - it'd be way too easy to exploit.
It was also a pretty last-minute addition, and I was running low on motivation at that point in the project (my first at this scale), so I never went back to rework it properly. Right now it's more of a sandbox item than something meant for serious gameplay.