I'm a fan of the big payment processing networks, but this stock looks like a tremendous value.When it comes to the payments industry, Mastercard (MA 0.04%) and its larger rival Visa (V 0.21%) are two of investors' favorite stocks, and for good reason. The two companies have an essential duopoly on the payment processing industry, and both are extremely profitable businesses. In fact, Mastercard has produced a 46% net profit margin over the past four quarters.However, if you're a value investor like I am, V ...