Well if you really want to break it down....let's see.
GM Gaskets...about $4 each maybe?
Bung Plug....again, only a few bucks from an exhaust shop
The exhaust clamps are going to run you about $7 each
Wire to extend the O2 harness....literally...just pennies right there. Cut, splice and ad about 20 inches to the current connector.
I got me a pipe expander at Harbor Freight....$13 and I did that part myself.
up to you really.