Al Franz wrote:
Have a gas fireplace that the back wall has the brick smashed pretty good
and has about a 2" x 6" hole in it. What type of cost should I expect to
fix something like this? Can just a part of the back wall be replaced or
does it require a whole new fireplace insert?

When you refer to the insert, what brand and model number is it? Many
times this can be found around the outside or just inside the lip of
the opening. Info will be on a plate riveted to the frame. If inside,
you will need a flashlight, rag, and good eyes to harvest the
information.
Repairs might be as simple as buying a replacement backwall and
installing it.