I read a comparison of CM and another service and it indicated there was a $5 charge per A/B split test.
If I have 10,000 subscribers and send out an email to all of them as an A/B split test (5K get A and 5K get B) is there an extra charge beyond what I'd pay for just a single email to all 10K?
Good question, and i'm happy to say the answer is no. From a billing perspective an A/B test to 10k people is identical to a single campaign to 10k people.
Pedantic nitpick: if you have a list of 10k people, you can't send A to 5k and B to 5k. The maximum you can send to during the testing phrase is 50% of your list, ie 5k people. So during the testing phase A can go to a maximum of 2.5k, B to another 2.5K, and then when the test is finished the remaining 5k will go to whichever of A or B wins the test.