Depending on the reason you cast the spell. If it's only because you want the money, then it most likely will not work. However, if you're doing it because you're actually in need of money, then yes it will probably work.
You could do a prosperity/money mojo bag and simply keep it in your house to attract money and prosperity, and maybe spread patchouli or cinnamon incense around the house.
In terms of how long they last, there's no definite answer, though from my experience, a money spell would probably work once for each time it is cast. Which is why I suggested the mojo bags, they can last a while, depending on what you put in.