
http://pages.ebay.com/help/sell/fees.html
You can find LOTS of helpful info using ebay's Help button. I typed in Fee Schedule and got the above link.
Auctiva's are estimations because sometimes they can't keep up with ebay's promotions and/or short term sales..for instance, right now if you offer free shipping, you get a subtitle free of charge which is normally .50 (I don't know if this is just for powersellers or not?) But when I create my listings, if I look at the estimated fees, it says I am being charged for the subtitle.
But check out the fee schedule...listing for .99 or 9.99 is always cheaper than listing for 1.00 or 10.00. This stuff is good to know

I myself never look at the estimated fees...I figure since I'm going to list it anyway, what's the difference?
Good luck!