You won't notice any real performance boost in normal driving. If you ran it hard (4500 rpms or so ++) you will get some small performance gains because it will be a little less restrictive. It will sound OK though.
You may not find a bolt on kit, or find out when you get it that the factory system is welded or now corroded together.
Find a decent local exhaust shop,tell them what you want, and let them give you a quote. It may not be that bad.
Like I said search, there a countless after market exhaust manufacturers.