"costed" is proper when referring to the past action of determining the price for something to purchase. "Last week Sheila costed out the parts list, so it should be accurate."

"priced" is proper for both the past actions of determining the price of something to purchase or something to sell.

"Last week Sheila priced out the parts list, so it should be accurate."

"Last week Sheila priced everything on the shelves."