Those Planets are great, I wish we had more of them!
It costs me 10 cents/(month*feed) for superfeedr to ingest an RSS feed; it fills up an SQS queue with content items which is a model I find easy because I can drain that queue at my leisure.
It would be very cost effective for me to add a Planet and have my recommender system discover articles I like from it, that is, I'm happy to ingest 1000s of items a day to my reader.
Nostr works on a similar basis but you push to the aggregator instead of them pulling.