You would want to get an axleback, as that includes the piece of pipe that bolts to the b-pipe.

The muffler has a pipe welded to it, that connects to a larger piece of pipe in the exhaust system via flange. If you buy a muffler, you will need a shop to weld it onto your existing piping. Waste of time.

Just buy an axleback that is ready to bolt on and save yourself some hassle. If you cant afford a catback, and just want something to replace your rusty muffler, go for it. In terms of performance...its all pretty much negligible on a basic NA setup.