Ok maybe my last was hard to understand, here is a more simple version to the question. I have a question Does it take a plugin to have a cash balance system in a paid url shortener service, for users? or is it only saved as a regular database integer just like id and password?
You are probably best asking that question at the support forum for the service you plan to use. It will depend on the database and script design. Which service do you plan to use?