I think if it's long standing friendships there's certainly more wiggle room. Even to the point that you ought to just be able to tell them to let you know if they feel you're being obnoxious about it.

But often it's also not even amounts, as long as it's reasonably discreet and you create a plausible excuse for why you're paying, and there's a sense of back and forth. With friends or girlfriends I know earn less, I've usually made a point of saying that when I choose or suggest where to invite someone, I prefer to pay and I'd appreciate if they let me, and if they insist on paying for something they can pay for things when they choose the venue. There's a tacit "because that lets each of us pick somewhere that fits our cost level" in it that remains unstated, and the give and take helps make it feel more even as long as it's not too blatant and in your face and you never make a point of how expensive anything you pick is. It also works best if you also pick cheap places sometimes.