Contractor indicates that all angle irons on the exterior of a brick cape cod are rusting/disintegrating causing mortar to separate and crumble at points. Places pointed out appear to be separating.
What is the going rate on such repairs?

If the irons were of quality steel,installed properly in the first place and maintained over the years,they shouldn't need replaced ever, but that's ideal for all points.

What are they doing exactly,is there a separation of layers of the steel?

Can you take a screwdriver and remove a half inch of rusted metal by prying on it?

Are there visible holes below the iron under the brick line?

Are the cracks in the mortar only from the edges of the irons?Or from all points between?

To add to KBC the biggest problem is going to Match the old mortar. Mortar samples needs to be done and totally cured to get the best match. There's nothing worse then a Patched look on brick.

To me it sounds like you are getting moisture build behind the brick work. Out in the field we use a strip of 15" felt tar paper and lap that over the back of the angle part behind the brick . We lay the first course of brick over the iron/steel and leave a couple of head ( vertical joints ) out. Theses are are referred to in the field as "Weep Holes"

Check for moisture build up before completing any repair on the angle irons or its going to fail again.