An ecojew is a person who is not Jewish in religion, but acts like a stereotypical Orthodox Jew when it comes to dealing with money. Examples of this may include being cheap when purchasing goods, counting money meticulously to the point of annoyingness, being stingy with money, or being very good at paying taxes. In extreme cases an ecojew may be the equivalent of what one would call a cheap bastard.
Phil: Hey you know that guy Charlie? He is SUCH an ecojew!
Dave: Yeah I know Charlie... I thought he was Roman Catholic.
Phil: No I mean like, I caught him converting all of his savings to quarters and counting them coin by coin to make sure it was all there.
Dave: Oh, I get it! Wow, what an ecojew.