I would think it’d be significantly cheaper to create and run you own than use AWS Lambda 
You could use something like:
…and host the service on a very cheap dedicated server (you can get them for about $40 a month now I think). You could them simply copy them over to your app or hotlink to them from a sister-domain or subdomain on that server. Large hard drives are very cheap now, so you could easily host up to 2TB for around that cost I reckon.
There are lots of good dedicated server suggestions in this thread on EF btw: https://elixirforum.com/t/deploying-elixir-opinions-on-heroku-digitalocean-bluemix-etc/289