If you got into an altercation and just happened to grab a Yamaha guitar to bludgeon somebody to death with, it would have been an expensive instrument.

That (entry level) Yamaha guitar would have cost you your freedom - if you'd got caught.

Similarly if George Bush was going to countermand the order to attack Iran, and reached for his mobile phone - but it was dark and he picked up a kazoo instead - that also might be considered an expensive instrument, in the circumstances.