Ask HN: How to deploy an AI App?

My mate and I are thinking of deploying a website (maybe running Node & Express), where users can upload an image. That image will be passed to a python script in the same environment, which will contain the AI logic / neural network. Then we want the image to be sent back to the front end.

We are looking for the lowest-cost solution as this is just a hobby project, maybe even a solution where the server starts up on demand when someone tries to reach the website.

How would you deploy an application of this sort, using what cloud service?