given the fact you appear to be looking to buy rather than sell, i would highly recommend fish.
Comfrey's have a specific use where you can boost them very high with suffusensing and this is what this iso is about:
https://forums.d2jsp.org/topic.php?t=105320359&f=273&o=0I can't say what they're paying as i never received an offer, but i would tell you i would want significantly more than the fish.
For fish, i'd recommend this guy as he's the only person actively bumping a topic to sell them:
https://forums.d2jsp.org/topic.php?t=105254022&f=273&p=668650902#p668650902As some idea for fish values, 1fg:700 life and 1fg:350 mana is roughly where we're at right now.
If you need a smaller stack he can probably sort you out.
In terms of the actual question, i'd suggest the life prices of good comfreys to be around 200life:1 fg and 700life:1 fg on low rolls. Not exactly sure where the price of mana comfreys is, probably similar ratio to the fish