There are lots of ways to accidentally spend too much money on AWS, and one of the easiest ways is by carelessly transferring data. As of writing, AWS charges the following rates for data transfer:
Data transfer from AWS to the public Internet ranges from $0.09/GB in us-east-1 (N. Virginia) to $0.154/GB in af-south-1 (Cape Town). Therefore a single terabyte of data transfer will run you a cool $90 - $154.