See this post. Buying them through the trade interface costs the right amount.
Tested with Omnifactory v1.11b (without Nexerelin). May be an issue with vanilla.
Robert Maguirerepo owner
Do you know what steps are needed to reproduce this? I can't seem to replicate this on a new save with 1.11b and vanilla, prices appear fine.
Hmm, damn, I coulda sworn it happened with vanilla + omnifac...
Anyway the issue seems to occur when an entity is assigned to the neutral faction, regardless of what the market or submarket factions are. So I'll work around this in Nexerelin, inform Alex on the forum, and this issue can be closed.
Ah, yes. I've had trouble in the past with the neutral faction giving things out for free, that's why the Omnifactory is owned by the player faction these days. I'm guessing when the market bug was fixed the refit screen code wasn't updated to match.