According to the NTSI list, you can expect to pay $667 for a 244 Opteron or $1333 for two of them. The 244 is a dual processor chip and is probably the 2.0GHz version. The list also includes a Newisys 1U dual processor Opteron system at $3467.
The link to the price list is on AMDBoard. µ
Also see
INQUIRER Hammer coverage