I guess I need to change/update my initial answer.
Least expensive that I carry and use now is a faux West German Cold War era Bundeswehr, at $5.98. Next cheapest is a Marbles MR278 "Demo Knife" at $6.98. Both are in my EDC carry rotation and get used.
Most expensive is a GEC 610211 half congress, or a (Stag) GEC 852211 Harness Jack.
Both the GEC's have been in my pocket and have been used since I got them a couple weeks ago.
I'm not sure which of the GEC's was the most exensive, they were gifted to me.
I'd guess the 85, due to the Stag covers.
I know both were $100-$150 each new in 2011.
I suspect if you could find one on the secondary market, they would cost considerably more now, than when new.
3rd most expensive would have to be a Case TB61028W DAM Mediterranean Blue Tear Drop, with a Damascus Wharnnclif blade. (also gifted to me)
I believe it was well over $100 when new in 2015, as well. I'm pretty sure the two GEC's cost a bit more though, since it is not a Tony Bose collaberation.
The Case has also been in my pocket and used since it arrived.
I always carry more than one knife in my pocket.
This week, I have six in my pocket plus two on my belt.
