Whenever my parents or friends give me raised eyebrows about how much a knife cost me (because they know I work retail and am not exactly rolling in cash) I am quick to mention how much value knives retain.
That $400 isn't spent as much as it is tied up. That knife can be sent in for free service for life, and can be sold a decade later for not really all that much below the price of a new one - sometimes more, if the older model has features that have been discontinued or are otherwise sought after.
I've never owned a car worth more than $1200. I've carried $2500 knives, used them, and then sold them without losing money. Knives aren't necessarily a great investment, but, if you're careful, they don't have to be extravagant expenses.