You may want to look into preserved farms that are going to auction. The price per acre will be
much lower than land with development rights. See our link on this subject:
Auctions of Permanently Preserved Farmland NJ State Agriculture Development Committee - PennJersey.info Forums
Susan Craft in the Ag department also runs the State preservation program and is a great resource. She could tell you about properties that they have preserved that meet your needs, but may not be currently listed for sale.
I also suggest that you join the NJ farm bureau if you have not already, and visit public meetings of your county Ag development board. Farmland is not often listed for sale even though farmers may wish to sell. We tend to be a bit apathetic since most of us have been burned in the past while trying to sell our land.