I have a customer going live in a week and all of their Pricing is based on Last Cost on the Item Warehouse Details record
Last Cost is not a selection by itself on the Calculate Pending Prices popup on Sales Price Worksheets, only Last Cost + Markup %.
I've had to work around that by creating a Business Event to update the MSRP field on the Item Warehouse Detail record with the last cost every time the last cost changes due to a new receipt price (their pricing changes real-time as costs change). Then use the MSRP field to calculate a new Sales Price record each time the last cost changes. They can have up to 12 different sales prices records for each inventory item due various pricing strategies.