IAM Certificates
HTTPS, SSL and TLS make the Web secure, which is an incredible feat. To secure your own app, you need to install an SSL certificate. Certificates cost between $50 and $400 per year, but you can test your setup with a free one. The terminology is complicated, but you only have to do it once a year.
The AWS documentation has a good explanation of setting up SSL certificates for use with the Elastic Load Balancer (ELB), which is what we'll be doing. It's quite an arcane process, so follow it very carefully step by step.
Vendors
There are many businesses selling SSL certificates, but you should only purchase from one you trust. Comodo and RapidSSL both have good reputations. RapidSSL is slightly cheaper, but Comodo offers a 90-day free certificate for testing your setup.
A certificate for a single domain should cost $50-100. A wildcard certificate can be used for unlimited subdomains, but costs about four times more. Thus a wildcard certificate may be more cost effective if you plan to have more than four independent applications.
What should I do?
Start with a free 90-day SSL certificate from Comodo. Follow the instructions of both Comodo and AWS.