WHA IS THE CHEAPEST WAY TO FIND AND PATCH UP A SMALL HOLE IN THE MUFFLER?

To find the source of the exhaust leak, with the engine running get a friend to block the exhaust for a few seconds with a fist full of wet rags or the sole of their shoe the gasses are hot so don't get burned. With the exhaust blocked off momentarily the exhaust forces out where the leak is and is easy to find.