AWS Lambda usage costs are a little tricky to understand, because the usage cost is per GB seconds of usage. This is calculated from the execution time of your Lambda by the GB of memory it is configured to use. For example, a single request to a Lambda configured to use 1GB that executes for 1 sec is 1 GB-sec.
AWS offers a free tier that includes the first 400,000 GB-s for free, and the first 1,000,000 requests a month for free. Above those you’re charged $0.00001667 for each GB-s and $0.20 for every 1M additions requests. Check the details here.
I put together a simple webapp that allows you to play with the numbers and see what your costs are going to look like. You can check it out (served from AWS S3) here:
https://s3-us-west-1.amazonaws.com/awslambdacostcalc/index.html
If you’re interested in taking a look at the source for the React app, it’s here on Github. Create me a ticket if you find any issues.