Apple has the Refurbished Mac Pro workstations on sale, shipping is free.
Refurbished Mac Pro workstation w/ Intel Xeon Quad-Core 2.8GHz, 3GB, 1TB $1819
Refurbished Mac Pro workstation w/ Intel Xeon Quad-Core 3.2GHz, 6GB, 1TB $2139
Refurbished Mac Pro workstation w/ Intel Xeon 8-Core 2.4GHz, 6GB, 1TB $2649
Refurbished Mac Pro workstation w/ Intel Xeon 12-Core 2.4GHz, 12GB, 1TB $3239
Refurbished Mac Pro workstation w/ Intel Xeon 12-Core 2.39GHz, 6GB, 1TB $4799