The Collaborative International Dictionary of English v.0.48:

Sawbuck \Saw"buck`\, n.
   1. A sawhorse.
      [1913 Webster]

   2. [Colloq., from the Roman X for ten, like the support of a
      sawbuck.] a ten-dollar bill; also,

   double sawbuck, a twenty-dollar bill.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Sawhorse \Saw"horse`\, n.
   A kind of rack, shaped like a double St. Andrew's cross, on
   which sticks of wood are laid for sawing by hand; -- called
   also buck, and sawbuck.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sawbuck
    n 1: a framework for holding wood that is being sawed [syn:
         sawhorse, horse, sawbuck, buck]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "sawbuck":
   C, C-note, G, G-note, buck, cartwheel, cent, century, clotheshorse,
   copper, dime, dollar, dollar bill, fifty cents, fin, fish,
   five cents, five hundred dollars, five-dollar bill,
   five-hundred-dollar bill, five-spot, fiver, four bits, frogskin,
   grand, half G, half a C, half dollar, half grand, horse,
   hundred-dollar bill, iron man, mill, nickel, penny, quarter,
   red cent, sawhorse, silver dollar, skin, smacker, ten cents,
   ten-spot, tenner, thousand dollars, thousand-dollar bill, trestle,
   trestle and table, trestle board, trestle table, trestlework,
   trestling, twenty-dollar bill, twenty-five cents, two bits,
   two-dollar bill, two-spot, workhorse, yard