sounds to me like you should get a moped
jk
but seriously yoru not gonna get close to 90mpg... 70mpg is gonna be tough. you might want to look for a buell blast. you could get one easy for 2k. they are reliable and easy to ride, they look half decent and the tanks are made from a material that you can buff deep scratches out of (because you probably will lay it over). and they get 50-70mpg.
keep in mind cities are full of traffic that does not see motorcycles, so you will have to be alert and ready for any car to pull out in front of you. i def suggest taking the motorcycle safety course if you dont have much riding experience.
oh and i dont suggest riding motorcycle after running a race. when your body is tired, you should not ride! i used to lift and ride home from the gym but i stopped when i realized how much control i had lost over the bike from being tired.
honestly, bikes are dangerous. i really suggest that you would look into getting something like a civic VX or something that gets 45mpg and you will still be visible to negligent drivers and old farts who run people over.