I had a couple of friends over for dinner last night and the husband knew that I collected kitchen knives. After dragging out a few to show him he asked me how much I had invested in these knives. I told him that I thought it was probably less than 10K. He asked me how I could spend 10K on knives and I said that it was my hobby. Now this guy's hobby is an airplane so he was satisfied with my answer.
I did a quick survey of my knives today and the investment is less than 10K, but not by much. I've been collecting knives for about 25 years so, on average, that works out to be around $400 a year. I spent way more than that on fishing trips (another hobby) during that time and thought nothing of it.
My point is that, as hobbies go, collecting kitchen knives isn't that expensive. I know that everything is relative but if you can afford it then "It's my hobby" is a good enough justification for a new knife.