Total Soviet Casualties for the Stalingrad and North Caucasus Defensive operations was 694,379 irrecoverable losses and 517,811 sick and wounded. Add in Voronezh-Voroshilovgrad Defensive operation for 36,883 KIA and 29,329 WIA. Stalingrad Offensive opperation (19 Nov-2 Feb) 154,885 KIA and 330,892 WIA. Total 886,147 KIA, 878,032 WIA/sick for grand total of 1,764,179 casualties!!
All figures from Krivosheev, Soviet Casualties & Combat Losses in 20th Cent.
However I don't think it is fair to compare blue and uranus to Tunisia (from german side) and IMHO the destruction of 6th Army is roughly comparable to forces lost in Tunisia!!