If one of those brackets is cracked, I'd have them carefully inspect each "traverse arm" (trailing arm) as well as I've seen those bent on a couple occasions, reasons unknown to me but I suspect due to side impact (some sort of accident).
The parts (arms) cost about $400 each and book time including alignment is around 8 hours.
I've never seen one of those brackets crack or break "by themselves" due to being dissimilar metals but if it's the brackets that I'm thinking of, requiring R&Ring the arms (both), then yes it's a big job and requires an alignment too to get rear toe re-adjusted. It's not a DIY job IMO as it may also require a torch to get the bolts out.
Don't be too surprized if they also discover bent arms, which can be seen by carefully looking at them from under the car (still assembled). They should be straight, not bowed.