I think the life expectancy for the stock exhaust systems varies according to
where you live.  Here is the north east I would say we go through them about
once every five years (from what I have heard from others as well as my own
experiences), up in Canada the life expectancy is probably less and out in
California and other very dry states with warmer climates they can last for 10
years or more.  I think the $750 is a very good price if you never have to
touch the exhaust system again (except when you have to remove to get to those
darn head gaskets <insert whining noise here>).
Ken Wilford
John 3:16