I help a lot of buyers and sellers in Fishtown. It is a great area. To answer you question, would need to know the block. Prices in Fishtown range dramatically, from "the heart of fishtown", "riverside fishtown", "fringes of fishtown", etc... Also, the property values will change dramatically north of York St and West of Frankford ave even though the zip code is still 19125.
Feel free to contact us for more info.
Also, visit our website at http://www.thesomersteam.com
and visit our fishtown section.
Good luck !