If you’re playing a non-Esper mutant and get the physical mutation Regeneration to level 5 prior to Golgotha, you can more-or-less ignore disease.

wiki.cavesofqud.com/wiki/Regeneration

I normally go for Regeneration just because (a) it’s so much of a pain in the butt to deal with fungal infections, and just at level 1, the mutation makes it mathematically extremely unlikely for incubation to complete and (b) gamma moths can inflict mutating and at level 5 or above, Regeneration has a reasonable chance of curing it before it completes incubation. Level 9 and it becomes very unlikely, though that’s a lot of points to spend.

Level 5 Regeneration has a 2% chance of curing a major debuff per turn. Mutating has a short incubation period, 100 turns. So your chance of incubation succeeding at level 5 is 0.98¹⁰⁰, or about 13.3%.

At Level 9, it has a 4% chance per turn. So the chance of completion of incubation of mutating goes down to ~1.7%. And there’s a small chance that mutating will have a beneficial effect even if it completes.

There are a few other ways of dealing with mutating, like becoming friendly with the insects faction to keep gamma moths onside or building a character that can stay out-of-phase, and I imagine a character with a high DV might also work.

rarest and most expensive one

Wine isn’t the rarest and most expensive liquid. It is more expensive than water, four times by volume. You can easily get it at the Six Day Stilt.

Cloning draught is the most expensive liquid, 1250 times by volume. Once you have one dram of it and a gyrocopter backpack (which can contain 128 drams of it), a late game strategy — tedious though effective — is to farm metamorphic polygel. Various merchants, especially Tillifergaewicz at Yd Freehold, have a (small) chance to stock polygel. Polygel can be used to duplicate any item in the game. Cloning draught can duplicate any character in the game, including Tillifergaewicz, effectively increasing the chance of polygel being available when you visit Yd Freehold after a restock. Once you have a metamorphic polygel, you can duplicate a container and all of the liquid it contains, such as a gyrocopter backpack and all of the liquid in it. If you have two containers partially full of liquid, you can pour all of one container into another (well, except for neutron flux, which requires special handling).