If you click on an item that's "out of stock", then click on a different item, it will show recently viewed items on the bottom (mobile site anyway). And when it shows these items, the price is listed on them. But if you click on it, it then just shows out of stock. Hope this makes sense?

Probably an internet search engine. If you do a search on "the exact item number and how it's listed" from Buds you get a search string. Usually when you look through it you can find an old listing/advertisement still on the internet when the item was in stock with price..