At the small volume of data where you could "just put stuff in S3 and search it later", the cost of tracing with a SaaS vendor is also very small. Far smaller than the developer time needed to set up something else.
I'm mainly responding to this point regarding developer time outweighing the cost of just going with SaaS vendor that provides that capability. I don't think we disagree with each other though
I was arguing exactly the opposite... leverage S3's near-infinite storage so you can store whatever you'd like. Searching through it _can_ be fast with the right tool.