Answer:
A rough approximation is that on the order of 2000 people total (both black and white) were killed during the Klan's coercive and murderous activities. The research cited clearly indicates that the majority of these died at the hands of the Klan in its earliest years, from 1865 to 1875. According to the Tuskegee Institute, about 1500 of the 2000 total killed died in that time period. (Understandably, as the Klan could operate much more freely in the disorganization that prevailed in the South immediately after the Civil War, as compared to later decades.)
The later renditions of the Klan (20th century) killed a much smaller number of people : a few hundred in the 1920's, a few dozen in the 1950's, and some single instances of murder into the 1970's and 1980's. As the number of murders imputed to the Klan dropped drastically, the likelihood that the perpetrators would be caught was also increased. With modern law enforcement, and the increased number of black police and public officials, the Klan could not operate with impunity.
* The total number of 3446 lynchings of blacks and 1247 of whites includes many groups in addition to the Klan. There is no doubt that the Klan was involved in the eviction or coerced relocation of many hundreds of thousands of freed blacks, and that the number injured by their violent acts was in the tens of thousands.