Most expensive - Springfield XD40 - Currently out of carry rotation due to oddball slide lock issue I experienced at the range. Probably the fault of either a dirty or mis-seated mag, but it happened twice. Enough to make me stop and think. I didn't have enough time to thoroughly diagnose it last range trip, next time I'll do some more testing.
Least expensive - Taurus Millennium PT140 Pro - Dead on reliable, never malfunctioned on me, even when shooting it in crazy conditions. (Dead cold, during pouring rain, crappy and great ammo.)
My Walther P22 should have the honor of "least expensive gun ever carried daily" but I overpaid for it by a long shot. The P22 cost me about 30 bucks less than my XD40 - I was uneducated, and had no clue about the worth of the gun.