I've seen this too confused me . when i was searching one day they was there for say 75 quid the next day a crazy emount !! ive seen this on the downpipes and sport cat like 2 grand. dont know whats going on there.
They hike the price when they are out of stock, that way advert stays live and they can put the price back when back in stock. It's just away of stopping people buying without removing advert