Be more descriptive please. A money system to go with what? Your statement lacks a predicate.

Im sorry but what i need is a money system where you acquire money by drops or by kills(each monster would give a different amount), the money will be used to buy better weapons after a night you will be able to buy, and im trying to make a zombie survival game with it and a money system would make it better for what im trying if you need any more information let me know.

How not to start a mod.

I believe Eisenstern (the RPG version of Sauerbraten) had something like this, though it was discontinued. Eisenstern was picked up and put on Sourceforge, so that it could continue, but it hasn't been touched in months. (SF project page.)

well since you cant set health, armor or ammunation by script you cant really use the "shop" system if youd script one.

except for keys and stuff

ok well thanks for the information

If you make it very cleverly, it would be possible without editing the source, but I guess it'd be a bit complicated ;)
I'm talking about setting all the monsters to a tag, creating a function that checks the amount of monsters left in short intervals and sets the amount of money you have to: ((amount of money per killed monster) * (monsters on the map - monsters left)) - (money already spent).

Then make a shop with a gui where each button triggers a door behind which you can find a piece of ammunition or health.

It's possible but I'm not sure if it's worth that :P