I got a cool old honda scooter. Still working on getting paper work for it and it restored. Just remember most of the 50cc and under scooters will maybe get 35-40mph, if that is within your means of commuting I say go for it. If I lived in the same city as my work, I would be scooter commuting for sure.
Also, if you stick with something under 50cc, you may not need to get a motorcycle endorcement.
Something used with a little milage on it is always going to be cheaper than buying new, and if you are trying to save money, the initial investment is a good place to start.
Here is a pic of the honda, its a 64 ish C110, or cub sport, or cub 50, whichever you feel like calling it It makes 5hp @ 9000 rpm according to the manual. Its gas tank was off in this picture.