As already mentioned, $4-$5 gets you a tiny instance all month. But, for me, I just run my small jobs on my existing virtual machines, generally speaking. I have a bunch of servers, they already have my necessary libraries, files, and database information and caching and such setup. Running a cronjob, or something triggered or pulled from a queue, is trivial and practically free.

My feeling on this is that if the job is small enough and infrequent enough, I don't care about its impact on other services so I can run it anywhere (and it's effectively free in such a case), and if it's large enough and frequent enough then setting up for it in Lambda every time is wasteful and I probably want a system (even if a small one) dedicated to the job, for probably less money. There's probably a sweet spot in there somewhere...but, it's not high on my list of things to integrate into my infrastructure.