A second suggestion to consider the Real Steel S3 Puukko Flipper. It has all of the qualities you specified, namely M390 blade, frame lock, flipper, 4.0 oz advertised weight and all for a nickel less than $155. In addition, it's a titanium frame lock and the blade rides on bearings. One possible issue though - the blade exhibits a dual grind, in the same spirit as the Spyderco Terzuola C174 Double Bevel.