I was wondering if there was an LDB that would show both your VendorTrash and Repair Bill. It would just look like this 15g07s08c / 5g18s00c. Has anyone seen anything like this?
There are other LDB displays to show your durability status.
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"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh
FuBar_DurabilityFu shows the cost to repair your items in the tooltip. The repair cost isn't different for each item; there is a known formula, at least for armor, which can be found on WoWWiki.
Addons don't know how much it will cost you to repair until you visit the repair vendor (unless they kept a large database and did a bunch of math).
You can use :SetInventoryItem() and :SetBagItem() to get repair costs (it is the third and second return values respectively). They're both functions in the GameTooltip object.