I agree that it could be reduced in cost and be balanced. Something to note is now it acts like a pillar until used and when used it adds 1 purify/antipoison counter to each of your creatures.
What cost do you think is fair for this card? (The new version)
Well, it depends.
Increasing the base cost makes it slower, but something like 4
, 1
to activate could be ok, considering you can regain the cost if you have it out for some turns.
I would prefer going with a more fast and genuinely useful 2
, 4
to activate (3 if upped). It costs as much as plague to activate it, which is ok, but it can be played easily even in place of some pillars. You can keep it out if your opponent doesn't use poison, and use it as needed. It would probably be more solid this way, and definitely not OP.
That's just my 2 cents, anyway.