Check out these Babies. While searching around the net trying to find out how to reline a motorcycle helmet I found these bikes. Gas crunch answer for you from 49cc to a 250cc V-twin and the prices aren't bad either, all with features of a larger bike. Way better than a Moped and cooler than a ton of those cheap china scooters to boot.
Their Kikker 5150 Hardknock Frisco Chopper is a kit bobber with all metal parts, no plastic bits they say, and can be had with either the 49cc, 125cc, 200cc or the already mentioned 250cc 4 stroke 4 speed tranny engine. You can find out lots more here about them http://www.kikker5150.com/hardknock.html
or the manufactures home page http://www.kikker5150.com/indexb.html