Suppose it depends upon guard units too. Lasguns and flak armour are probably cheaper than guardsmen, and are reusable where guardsmen normally aren't (though they can be re-purposed as servitors upon first death).
The basic Cadian pattern guard kit consists of a lot more than is on the normal models if I remember right. It includes several sets (2 as I recall) of fatigues, a knife, field rations (usually corpse starch or similar in a self cooking package,) a canteen, a backpack, several small storage pouches, 1 frag grenade, a bedroll, boots, and of course the most important thing:
toilet paper the
Imperial Infantryman's Uplifting Primer. Lasgun/lascarbine, flak vest, shoulderpads and helmet of course, with 3(?) las cells.
Optional additions include com beads/portable vox, additional frag grenades, krak grenades, auspexes, weather protective clothing, protective/augmentive goggles, grav chutes/parachutes, rebreathers/gas masks, blah-de-blah-de-blah. Tons of stuff that some regiments issue as standard, but Cadia and imitators usually don't bother with.
As much as we often imagine guardsmen being deployed as modeled on the tabletop they do actually have a bunch of junk that you'd expect a soldier to have. Usually leave it stowed on transports or in camp if allowed, but it's still issued.
A drafted ganger, prisoner or feral tribesman is probably worth less than even the standard loadout, partly due to being a drain on resources normally. There's plenty more just like them where they came from and despite often already being decent combatants they're still 50 to a penny as it were.
As for the rest of that, yeah pretty much. The guard are the Hammer of the Emperor after all. Brute force and weight of numbers eventually solves most problems. Provided you have the ability to reinforce your guardsmen, which is surprisingly uncommon because of how much the navy has on it's plate, you can throw an arbitrary number of men at any problem.