The following players, IMO, could potentially be both extremely cheap and surprisingly decent. This isn't a list for buy-lows like Shark, Latos, or Ian Kennedy, who could be very good and will likely get decent money. These guys are best thought of as #6 SP candidates.
The (s)hit list: buy low free agent pitching targets
Trevor Cahill
Bud Norris
Tim Lincecum
Doug Fister
Kyle Lohse
Gavin Floyd
Brandon Morrow
Joe Blanton
Rich Hill
Edwin Jackson
Chris Young
I would love to get Cahill or Morrow to start the season in the pen, as the #6 SP.