Gracias Julia, que complicado es a veces...

I think they really said "you know, might not have even been no money." This is incorrect English but it is the way some people actually talk. The correct way to say this would be "You know, it might not have even been any money." You have another sentence there too. "I'll lay low and call Joe." To lay low is to hide and not be seen.

thank you!, I had a lot of troubles understandind that film..

The man is speculating that there may not have really been any money at the crime scene when the events happened. In a lot of English courses they will tell you that the double-negative does not exist in English, but it does. It is used often in commonly-spoken English such as the English that is used in the movie. The Coen Brothers are famous for having very realistic spoken English in their movies along with pronounced accents.