Decreasing expenses to increase wealth - Stocks

When choosing a broker to handle my stocks, I switched from A. G. Edwards Company to American Stock Transfer in order to save money because there is no service charge for reinvesting or adding money to the investment. For Zweig, there is always a cost to any investment. For most people, it is hard to tell what the fees are because, like myself did not ask the right questions. In this case, I asked if a cost was associated with reinvesting and the answer was no. In this case, a cost did not occur when dividends where reinvested. However, when you add additional money to increase your investment, a cost incurred when adding money to purchase additional stocks. Nevertheless, what I found out, I should have asked the question, if I want to reinvest by adding additional money is their a cost?