Well, I noticed that mithril arrowtips don't sell. Ever.
So instead I am doing mithril bolts.
The total cost of a bar is 852, the amount gained back from bolts is 830.
Therefore I lose 22 per bar, which is a total loss of about 280k.
I also now have 2.5m or so in junk (mithril arrowtips), which might come in handy...