My own $.02 in terms of changing this yourself is that if you could you probably wouldn't be asking. What is your level of mechanical ability? Tools?
The issues have to do with all of the rust & heat - these things practically become welded together; there's often not much room to work; it probably has to be done from underneath. Do you have access to a lift (best)? Or at least jack stands or a set of ramps?
If you can get the car up in the air safely and have decent mechanical ability and maybe access to an angle grinder you may be able to swing it.
But then again, I had one changed out but it is welded inline in the pipe. So it had to be cut out & a new one welded in. I paid all of about $150 at a muffler shop.