Pay what? Is that "Choose one - gain 2 life, or lose 2 life"?

That is correct

i understand why you've set this card up the way you have - the idea is that with bargain enablers out paying life suddenly becomes more worthwhile. the problem you've got is that in a vacuum, this card looks silly and that means it needs synergies to make sense. personally i think that's leaning too much on them when there's an easy way to fix it: make them do both

example:

First strike

Bargain (When this creature ETBs, you may pay life equal to its CMC. If you don't, gain life equal to its CMC.)

Whenever you pay a bargain, target creature gains first strike UEOT.

Oooh, yeah I was having trouble with bargain templating. That sort of style was my original intention.

Waht does 'bargain with' mean? 'Pay a bargain' is probably what you mean, right?

yeah pay a bargain makes sense if you want it to trigger on all bargains, and pay ~'s bargain if you only want it to trigger on sellsword's one

an interesting idea would be to have the latter at common and the former at uncommon

That was my thought, with the exception of Greedy Imp.

I might place bargain with CARDNAME and bargain with a creature at common, bargain with a creature and pay life at uncommon, and then pay life and gain life at rare.

i think that's probably being too clever by half, at least for now. and having a specific iteration of a key mechanic at rare only comes across if you're looking at the spoiler, you'll never figure it out by opening packs. IMO start out with two variants split at common/uncommon & rare and see how it plays