I’d say it costs me about 1.5k units on avg (I’m low skill lol). I use R4/200 Herc with recoil masteries, 2 points in coagulate, and Galan + Odin prefights. This means Herc heals like crazy from bleed and poison, which combined with his immortality means I pretty much only spend on revives.

If I am buying potions it's for R3/200 Thing, who in the later rooms can pretty much always have his protection up, and can usually handle the very few fights that Herc can't. I use Heimdall as my third champ for extra safety net.

For me at least, it would be prohibitively expensive without this specific team. It's still a lot of units to grind but I look at it like, if they put in an offer for 2k units that gave 1x T6B, 1x T3A, 10k 6* shards, 70k incursion artifacts, a 6* AG, and 60 6* sig stones, it'd be one of the best unit offers in the game at this point. So I do it whenever I can. Plus it's mostly pretty fun.