Transaction costs refer to small convenience fees charged when paying online via credit card. Specifically: - PayPal takes 2.9% of the program cost plus 30 cents per transaction as their fee. - StadiumRoar keeps an additional 1% of the program cost to maintain their software and donate to sports programs. - These fees are low (3.9% total) and people overwhelmingly accept them for the convenience and security of online payments versus checks.