It all depends on my reason for buying a particular knife. If I'm buying for the "nifty factor" and really like the design, I weigh that against factors like materials, country/factory of origin and scarcity; anything over $75 or so needs to have something special going for it, with around $200 being the upper limit. For instance, seeing a ZT 0801 for the first time was love at first sight, and although I paid close to MSRP (gun show, pre-MAP enforcement) I have no regrets. It is, in my eyes, a textbook example of a beautiful design, sort of a "time capsule" piece for me. Same with the Benchmade 760 LFTi, Kershaw Groove and a handful of others.
On the other hand, most of my EDC folders are well under $50, and a couple of particular favorites were around $25, although a couple were over $100. Regardless of price, if it's in the rotation, I trust it to perform typical daily tasks. Same with most of my outdoor-oriented fixed blades. I have spent around my $200 limit on a couple of them as well, but would just as likely use one that cost half that or less for the same purpose.