Hmmm...I'd say

battlefield troops~ 25,000 - 50,000 (Vipers/EEls/specialty Vipers)

Blue shirts(Techs/general Laborers that can fix toilets/do electrical work etc and then pick up a gun and fight, what I see as the civilian militia in Cobra towns) ~ 50,000 -100,000

Top Level Undercover (Seigies, spies, Sypathizers) ~ 2,500

Collaborators and people being used for intell and don't realize who they are working for ~ 100,000 or more

Merc's (At the high point) ~ 5,000 (To include Zartan/Dreadnoks/ Bludd/Firefly/Raptor, etc)

Iron Grenadiers ~ 5,000