If the OP is open minded, perhaps shop for a vintage quality ATB bike. Far larger selection of small framed, higher end tubed bargains are out there for conversion. Do some wheel / 26" tire magic or go for 650b swap. Custom suit to whatever, from drop bars, stems, shifter type's etc..
edit: A bonus having a small frame and should easily get into the sub 20 pound with a carefully thought build and very light 26" wheels.
Last edited by crank_addict; 07-23-14 at 12:08 PM.