I think I may get a motorcycle someday.
I'd save a lot of money on fuel.
But you'd waste the same amount of money on closer service intervals unless you work on it yourself.
Basically: If you live in an area where you can ride all year, and if you don't need to own a car, then economy may be a reason to consider a bike. If for whatever reason you need to own a car too, then economy is a bad reason to get a bike.
To make the commute more interesting, to experience nature closer and to have fun are pretty valid reasons, though.