At the same time I bought a new MacBook Pro, Canon 5DMkII and 70-200 2.8 - can't remember which of those was the most expensive but think it was about £5k overall
For me though it's hard to say what the most expensive thing I've ever bought is. Spent about 18k on my hifi, but that's not a single item. Have a couple of watches that were > 4k each so one of those could be the most expensive single object, maybe.