If you look at the Shops link on the NYMSTF web site you'll discover there are only two shops downtown and one is just a small Vespa store which does not perform any service. The other shop is a small independent shop called Sixth Street Specials, at 703 East 6th Street. They specialize in Brit bikes but do other work as well. Being an independent shop, they are more likely to have reasonable shop rates. I can't speak for their quality personally but they do have a cult following.
[EDIT] I just noticed your post in the other topic, which mentions you're seeking to have a Vespa serviced. Jillian has good advice there.