When an item sells out and the Seller has no stock......and it may be some time until they have more stock, the price shoots up to a silly figure.....I don't know it it's automatic or the Seller does it manually.
It does this so that the Seller doesn't have to pull the advert and have to redo it later when he holds more stock........and and we all know how long it takes to put something onto E Bay !
I asked the question of a Seller some years ago and that's what he told me anyway.