Bank's Costs to Foreclose (specifically auctions)

I have a question regarding costs that banks may incur when foreclosing and taking it as a REO (“sold back to mortgagee”).

I am almost done with figuring out all costs associated with bank’s foreclosure, repair, and later sale as a conventional property. However, I do not know how to figure out auction costs.

How much does it cost to a foreclosing bank to auction a property? Are there set fees? Commissions? Little bit of both? Does it depend on the successful sale to an actual buyer vs. bank taking it back?

ANY insight will be highly appreciated !!!

Anyone have a good answer for this?