Anyways, here we go, Imperial Guard through the ages! We'll also look at how much the cost of special weapons changed throughout the editions:
Rogue Trader era!
2nd Edition! The Dawn of the Modern IG
2nd Edition was the era of some Truly horrific models. There's a reason nobody fields 2nd edition Ork, Tyranid or Space Marine models anymore. IG is the glorious, beautiful exception to the rule. Tallarn Desert Raiders, Ice Warriors of Valhalla, Mordian Iron Guard, Praetorian Guard and Cadian Shock Troops were all sculpted for 2nd edition, and in my opinion have held up phenomenally well for all that time. Catachans too, buuuuut.... they've never been my favorite. Though I guess the metal models looked about as good as their mediocre plastic counterparts. Truth be told, I still prefer these old school Cadians to the new plastics.
The army wouldn't look too terribly different from a modern IG, other than it being FAR far smaller (a 1500 point list included in the codex has like, two or three vehicles, and less than 50 infantry, which strikes me as absurd.)
One of the biggest differences, and most interesting to note, is the role of the Imperial Commissar. In this edition, Commissars lead by example, inspiring their men and overseeing morale... Without executing a single one of them. The Grim Darkness of the Far Future was still rather shiny in this era.
A bare-bones Imperial Guard infantry squad cost 100 pts, and a Heavy Weapon squad (3 teams) cost 60 pts, with the cheapest option being Heavy Bolters, at 10 extra points EACH.
Flamer (7) Grenade Launcher (10) Plasma Gun (6) Melta Gun (6) Sniper Rifle (n/a) Power Sword (6) Power Fist (10)
The Armageddon Steel Legion:
This gave us the great fluff for the 3rd War for Armageddon and Commissar Yarrick, and Colonel Schaeffer's Last Chancers. Good stuff. This was also the point at which I started playing 40k. Commissar's gain the Summary Execution rule, everything gets a little cheaper, but Guard truly suffers from the ability to leap straight from one victorious combat into the other. That's right, those damned Khorne Berzerkers can eat your sacrificial squad of guardsmen, and then immediately assault right into another one. Never mind that I can only fire at most 2 shots from each lasgun per turn, IF I STAND STILL (3rd edition was NOT kind to shooty armies), those khorne berzerkers could get to roll 3, 4, 5, hell maybe 10 or 12 attack rolls in a turn, maybe even more if they just keep slaughtering things. That's fair, that's REAL FAIR.
*cough* moving right along...
A bare-bones IG infantry squad cost 60 pts, a heavy weapons squad (3 teams) cost 35 pts before weapons, and the cheapest is the Heavy Bolter at 15 pts each, for a total of 80 points.
Flamer (3) Grenade Launcher (8) Plasma Gun (8) Melta Gun (8) Sniper Rifle (n/a) Power Sword (10) Power Fist (15)
Late 3rd/kinda 4th Edition: The Modernization/Focus on Cadia begins
This was also one of my favorite guard codexes due to the inclusion of Doctrines. You could super-customize your regiment with special rules, give them close combat bonuses or shooting bonuses, make them all drop troops (an entire IG army deep striking, just picture it), or chem fueled penal legions, storm troopers as troops, the list goes on and on. This was one of the IG high points, especially since it includes rules for Ibram Gaunt, expands on Schaeffer's Last Chancers, introduces Creed and Kell, the two great Cadian Heroes, and special weapons get a bit cheaper.
A bare-bones IG squad cost 60 points, and a Heavy Weapons squad cost 35 pts + weapons (the cheapest being the Heavy Bolter at 15 pts each again, for 80 pts)
Flamer (6) Grenade Launcher (8) Plasma Gun (10) Melta Gun (10) Sniper Rifle (5, but you have to buy Light Infantry doctrine) Power Sword (5) Power Fist (20)
A bare-bones IG squad cost 50 pts, while a heavy weapon squad of three teams cost 60 pts with a mortar (the default armament) with upgrading to heavy bolter (which was cheapest for all the other editions, and therefore the benchmark) being 5 pts each, for a grand total of 75 pts.
Flamer (5) Grenade Launcher (5) Plasma Gun (15) Melta Gun (10) Sniper Rifle (5) Power Sword (10) Power Fist (15)
The Valkyrie/Vendetta is scary/powerful, and possibly one of the first OP IG units. Personally, I really missed the wider array of options given us by the Regimental Doctrines, and I've really hoped they'd put them back in for 6th edition. Only time will tell, and we all look forward with bated breath to the new codex, no matter how much we might despise the name change:
IG regiments range greatly in size depending on author, home world, and edition of the game. In the 2nd edition, a regiment was made up of Every soldier that home world drafted to the IG at that moment in time. Not multiple regiments, but one single huge one. So in Eisenhorn, the 50th Gudrunite Rifles is literally 750,000 men, while the Tanith regiments (from the era of 3rd/4th edition) were 2,000-2,500 men each upon founding, oy. Granted, they were designed to function as a unified fighting force, operating closely together.
Steel Legion regiments canonically are about 2,100 men (12 companies of 175 soldiers), while Cadian regiments are 8,000 pairs of boots on the ground. It seems to me that strength wise, it's better to think of an Imperial Guard Regiment as having the fighting power of a modern Division, even if they tend to be far more specialized.
Combat operations involving huge numbers of troops, upward of 20 regiments or whatever, are never addressed as being organized into larger fighting formations than 'regiments,' but logic would dictate that, to coordinate these forces, the regiments are brigaded together under a higher commanding officer of the Departmento Munitorum. Like in the American Civil War, these brigades would be known by their commander's name, Hook's Brigade or whatever. Alternatively, the would be called after their Battle Honors (The Iron Brigade) or if they were all/largely drawn from the same place, they could take the appropriate name, re: the Irish Brigade. So for larger operations, several regiments would be grouped together like that. It's not a big deal, and it's never addressed in the fluff, but my way seems logical, and I feel like the fluff ought to mention something along those lines.