Welcome to the site.
Don't touch the exhaust. It will never sound much better unless you dump some $$ into it, and even then it's subjective. The 3800 just sound like crap with most aftermarket exhaust systems. Nature of the beast.
If you're not a wrench slinger then it's time to learn. Paying a shop to do the work you're looking for is going to get expensive fast. These cars are not hard to mod if you have a basic skill set.
I'd start out by making sure all the normal wear items have been addressed and have a solid base to start with or you're going to be fixing it as you go along which could turn into more $$
