The most I've ever spent on an EDC knife to date was $155 or so for a Spyderco Chokwe. Gorgeous, but way too obtrusive for discreet everyday carry and use in my office.
In terms of "dedicated one-hand-opening" folders, the least-expensive knife that I've been fully satisfied with is the Ontario RAT 1. A very functional flat-ground AUS-8 blade, 3.5" of length is big enough to do real work with but just small enough to not freak people out, good ergos, easily pocket carried (not too heavy, thick, bulky, etc), and all this for $28?!
However, no matter what "primary" blade I may carry on any given day, my trusty Vic Cadet ($20) has been my constant companion for the past three years. If the chips were down and I had to jettison all but one of my knives, the Cadet would be a very strong candidate to keep.
Nevertheless, I've yet to find a knife that stopped me from seeking "the next best thing" (currently a Benchmade 930 Kulgera) or my ultimate unicorn (Spyderco Kopa with the stacked wood scales).