As the other poster who replied to you showed, it's actually incredibly cheap. Additionally, it's perfectly elastic. That expensive hardware you provision or buy for your server that can handle this task (at a much, MUCH slower rate) would cost you significantly more. In addition to the cost of the server and running it, you also have a much harder job developing it. If we're talking about multicore, you're now managing the job concurrently on a single machine, and need the code to facilitate it.

I also feel like your comment is implying that the outcomes of the lambda option vs the worker server are comparable. As mentioned, the worker machine will still run in hours, rather than less than a second.