Ask HN: A good open-source version of Flatfile?

I keep seeing ads for Flatfile, and they just raised some absurd round.

The service is super nice, and really useful. The problem is the price tag — as an indie developer, I can't afford to spend upward of $50k a year on a service. The other thing is that I don't need 99% of their features... I kind of wish they did Cloudflare's tactic of giving away some low hanging fruit.

I've seen other open source options on Google but none of them have stuck out to me. Or better yet, what is everyone's go to data cleaning/fixing/mapping solution for uploaded JSON and CSV files?