That's crazy! If you're inclined to keep it, Rockauto [0] is a cheap place to get auto parts, and often cheaper than the local stores for the same stuff. $368 for a Walker cat for an '08 Element [1].
I know that some repair jobs can be a lot because of how modern cars are designed, but if the labor is a couple grand (sounds like it is), that sounds extreme.
[1]: https://www.rockauto.com/en/catalog/honda,2008,element,2.4l+...