Inventory valuation opportunity

We got a great deal on eBay and bought a good sized amount of items for our inventory at bargain basement prices.  Normally I would cost them based on what we actually paid, probably using ratios of normal list price to our purchase price for each item.

But...we use average costing for our inventory.  Our IT guy has created searches and reports for items where the sales folks can go in and see the last prices we charged our customers and also the last price we actually paid for those items.

We don't want the sales people to get used to the low prices that average costing would produce until the last item was sold.  So how can we overcome this and show "normal" costs for our inventory, but not inflate the GL and financials.