Ask a Southwest Airlines representative about the cost and size restrictions to check your bike on board and their first response likely will be, "I don't really know."
We know. We looked.
First is cost. $75 EACH WAY. So yes, you may have booked that non-refundable ticket and now you have another $150 add-on. In the old days, if your case met the size guidelines, it was free. BUT, the size guidelines were completely unrealistic, so you still had to pay up.