$65 for a Mangled Mac sounds like it may be worth it; you can buy another 3,1 and use the MM for spare parts including the RAM.
http://www.macofalltrades.com/Mac-Pro-2x-2-8GHz-QC-Xeon-Early-2008-p/mp-28-8c-e08b.htm
You'd be better of with a 4,1, though with a few upgrades, the lowest-end 4,1 can be converted into a 5,1 hex that is faster than the base 6,1.
http://www.macofalltrades.com/Mac-Pro-1x-2-66GHz-QC-Xeon-Early-2009-p/mp-266-4c-e09a.htm
http://www.macofalltrades.com/Mac-Pro-2x-2-8GHz-QC-Xeon-Early-2008-p/mp-28-8c-e08b.htm
You'd be better of with a 4,1, though with a few upgrades, the lowest-end 4,1 can be converted into a 5,1 hex that is faster than the base 6,1.
http://www.macofalltrades.com/Mac-Pro-1x-2-66GHz-QC-Xeon-Early-2009-p/mp-266-4c-e09a.htm