Please tell me what's the name of the metal wrap
combining Kris and Ecnerwal's answer that's a &quot;cap flashing&quot; cost is off topic.
Usually these are made to order at sheet-metal shop (ask at a plumbers supplier)
when you go to place an order (with a drawing and dimensions) they will tell you the cost.
It may be that the incorrect method has been used to make this connection and that a join capable of moving is needed here. It looks intact if it's not corroded, possibly only the join needs to be replaced with an expansion joint.