With Elastic Load Balancing, you only pay for what you use. You are charged for each hour or partial hour your Elastic Load Balancer is running and for each GB of data transferred through your Elastic Load Balancer. You will be charged at the end of each month for your Elastic Load Balancing resources actually consumed.
As an example, a medium-sized website running on 10 Amazon EC2 instances in the US East (N. Virginia) Region could use one Elastic Load Balancer to balance incoming traffic. If the Elastic Load Balancer ended up transferring 100 GB of data over a 30 day period, the monthly charge would amount to $18 (or $0.025 per hour x 24 hours per day x 30 days x 1 Elastic Load Balancer) for the Elastic Load Balancer hours and $0.80 (or $0.008 per GB x 100 GB) for the data transferred through the Elastic Load Balancer, for a total monthly charge of $18.80. Partial hours are billed as full hours. Regular Amazon EC2 service fees apply and are billed separately.