I got estimates from Triangle and from Johnson today. $1258 and $1186, respectively. There aren't any used or reconditioned bumpers to be had anywhere, so a new OEM one has to be procured. They're expensive, roughly $700.
I have an appointment with Performance tomorrow, but need to reschedule it already due to a work conflict. The woman who answered the phone was pretty impolite, so that's not off to a great start.
The Triangle guy was way more thorough, but he confused me. The bumper has a strip like a rub strip on its outside, painted the same color but replaceable. That piece is physically reusable. So the Triangle guy said what they would be doing is painting the large bumper, which would be new, and putting the old trim piece over top of it. That's going to look awful, because the paint's not in great shape on the existing bumper. It's dull and kind of peeling, and would look absurd on a brand new, freshly painted bumper. I tried to explain that this was no good, because while the existing stuff looks dull, it's at least uniformly dull, but the estimator didn't seem to understand.
Neither shop seemed to be able to make sense of the computer diagram of how the bumper went together. The Triangle guy at least called the MB dealer for help - the Johnson guy sort of picked whatever he thought "must be it."

I'm a little unsure what I'll do at this point.