I've been real happy with
my motorcycle.
The frame is a little beat up, but getting parts for it has been no problem. All of the medium-size Japanese motorcycles in the early 80's practically had interchangable parts. Also, insurance is really cheap on an older, standard motorcycle.
A sport bike like a Kawasaki Ninja is also a great candidate for an EV conversion, although a little more to insure, they look great and are very light weight.
Mine was originally a 440cc engine. You may just want to make sure to get something with passenger pegs. If it's big enough to carry two people, it's big enough to carry you and some batteries.
Also, look for a frame that has two pipes forming the lower part of the frame. That way, you can build a little frame between them to hold the batteries.