The most $$ knife I carry is my Darrel Ralph Krait, which is also my most $$ knife, period. I never thought I'd bring myself to carry it, but he insisted that they were made to be used (and can be totally refinished), and now, well, I'm addicted. Rarely leave the house without it.
'course, I tend to also carry something by Spyderco or Benchmade, or Boye, that would be willing to sacrifice itself to protect the Krait, if I had to cut something really icky.
Related to James' point, I went through many pairs of cheap sunglasses, before getting a $80ish pair of Serengetti Drivers many years ago, which I still have. Point being, I find often the experience of breaking/losing cheaper things doesn't translate over to the really nice things, because you tend to be more aware of them, and in some cases, they seem to become a part of you.
-- Carl