There may be some simple ways to test for exhaust leaks. Maybe pour some liquid soap, 50/50 water, around the pipe joints in front of and after the cats, start the car and look for bubbles. although it will smell REALLY bad once it starts cooking off. Small exhaust leaks don't make any noise really, but as the pipes get hot, the gap can get bigger.
You can also have someone cover the ends of the pipes one at a time with something and listen for an increase in noise at the suspected leak area.
You can have an exhaust leak fixed almost anywhere, if that is what it is. I wouldn't want to guess at a cost, but it can't be a lot. Of course, if it is a break, and not a loose joint, there may be a new piece of pipe to buy. The welded joints can break from rust after a number of years. Years ago, I had a flange bolt break at the joint between the header and converter inlet pipe. The other of the two bolts was so badly rusted, I had to hacksaw it off and re-drill the holes in the header flange to repair it. Another time, I had a muffler inlet pipe completely break off the front of a muffler.
130 total pounds of Pitbull ruled by 8 pounds of cat.