The other "unofficial Chinatowns" are in Flushing and Brooklyn NYC which are all linked together through this shuttle bus system. For a mere $2.50 you can catch one of these buses that leave every half hour or whenever it gets full. It's cheap and convenient.
Many people outside of the Chinatown community have heard of the Fung Wah Buses which run from the NYC Chinatown to the Boston Chinatown. I think right now for a round trip ticket it is about $25 which is about what you would pay for a cab one way from Chinatown to the Upper West Side. $25 is so ridiculously cheap. You can buy tickets right next to the Buddhist Temple on Canal and Bowery.
Another bus company that runs between Boston and NY's Chinatown is the Lucky Star. My friend from Boston says that since less people know about this bus line, lines tend to be shorter.
Similar deals can be found for places such as Washington DC, Philadelphia, and Richmond Virginia. You can buy tickets under the train overpass on East Broadway & Division.