Not a lot of 49ccs will do 55mph. The Aprilias will, but they are over $5000.
If you're looking at a 49cc specifically for the registration allowances, you gotta do your homework. There are more to those laws than "49cc or less is ok to not register". They also take into account intake systems, exhaust restrictions, braking and fuel mixing devices. Then a lot of states won't let you run anything on the road unless it's insured. Some insurance companies won't insure unless it's registered, and you can't register it until you get a licence.
It's not as easy as everyone makes it out to be. The easiest thing is to get the bike that does, mechanically, what you need it to do and then get the licencing and insurance (You should always insure things like this)
Once you let go of the notion that scooting won't be free.. you'll be open to make proper decisions of which machine you'll enjoy. Genuine makes a lot of good scoots, and then you can go creme de la creme with a Vespa and enjoy it for YEARS. Genuine also makes a high quality machine, like the Rattler 110. You can also check out the Vespa copy machines (They are really Vespas) like the Bajaj models (Those are literally tanks) or the Allstates. The Yamaha Vino is nice too.
There are lots of things available in the world of scootering, more than motorcycling by far. Do your homework and don't be one of those people that gets stuck with a 50cc because they think they are saving a bunch.
Also, if a 50cc is really your thing, check out the Derbi GPRnudes (I put up a post a few months ago in this forum)