Just stop tweaking, leave the FI drop rate.
I dont see problem here. If u need to enter in caves and spend 20 fsp to get one EW potion, than the price of potion will be 20 or more. People who hunt with this potion will still use it or will use lower. Economy will be stable. It should be rare potion and it should be expensive.
also not quite true in reference to the economy. Using lower level potion makes the price of that item go up and the fact that a scavenging drop rate reduction leads to fewer people doing scavenging leads to higher marketplace prices.
It may not be a huge problem - people will handle it one way or the other for sure - but it definitely does not keep a stable economy
It's not fewer people doing the scavenging that will bring prices up, just the reduced droprate. And won't stop the economy going stable again, once everything has settled down.
Increasing the droprate to somewhat under the rates as they used to be isn't going to hurt the whole community that much.
Increasing the cost of the UB 190, which with distil acts as UB200 which was not supposed to exist anymore (and used to cost 10 fsp before) would limit the use of it, so more breaking of gear that was made exactly with that idea in mind.
Increasing cost of Do750, will bring more people to use the inventable Do500, so more interest for inventors & farmers. If people really really need the extra few minutes gained by the higher doubler, then they will pay a higher price, having it become a virtually standard buff was not needed.
Increasing cost of EW's, will bring the EW1k up in price again, sure, so maybe that will get used less in situations where it wasn't automatically needed either, and also constitues a goldsink.
So that leaves EA, SES and FI800 pots. EA200 isn't enormously more interesting than the buff for most players, and SES potions were hardly used (unless as a back-up). FI1k potions being very cheap, made the FI800 redundant as well, if there's an increase in the cost of FI1k, then FI800 will become slightly more interesting again, bringing a bit more income to scavengers.
Maybe bring out a few more inventable or scavenged ones, like EW500?