What is a normal monthly fee for a bookkeeper to charge?

Bookkeeping charges based on Revenue is a poor system. One client could sell his items at an average ticket of $10 and sell $1 million per month and want each sale recorded. Where another client could make a single $1 million sale every quarter. Which client would take more work? If we just charge them based on revenue, would this be a fair market for doing each clients work? Your billing should be based on the work that you will need to do. A good rule of thumb is 50 cents per transaction and then add $100 for the preparation of Financial Statements.