Might I highly recommend checking out petfinder.com or your local shelters? Amazingly enough, they do frequently have baby turtles for adoption. And also remember, within the first 2-3 years, your turtle will have potentially outgrown a 55 gallon tank. So don't think that by getting a baby you are delaying the inevitable. My turtle was 6" by her second year with me. She has significantly slowed in growth now, but she shot up to that 6" very fast.
I got her at a street fair in NY. Baby turtles are really not that hard to come by. However, they are more than likely ill due to the conditions they are kept in, etc. I was fortunate to have gotten a healthy little baby, but I also attribute part of that to the secluded area that the street fair was at and the "vendor" seemed to be a backyard breeder who only went to that event.
But not everyone is reputable ... Reptile expos are a great place, as well as Craigslist.
Starting up a tank, it will cost around $500. So you may want to start buying things for the tank now just to be ready.
