The problem with most of these is cost. HeroForge is the biggest transgressor; I am not paying 25 pounds (around USD40, I think) for one miniature. Yeah, it's a custom mini, but I am not made of money. That's why I suggested HeroClix; you can get most of these from bargain bins at your FLGS, if they do that sort of thing.
Another option if you're worried about price is old Star Wars Miniatures figures, though you won't find any figures for trolls or dwarves (unless that Rat Shaman dwarf in your game really looks like a Jawa or an Ewok). Clone troopers and stormtroopers make for good security forces, though.
Another option is Reaper Bones; they're cheaper than metal miniatures and do have many options for sci-fi/modern settings. (Though painting is required, and some minor kitbashing may be needed to turn a larger figure into a troll.)
A LONG time ago, in the 90s, a toy line called XPanders had a product with 20 pre-painted (well, each figure was in one base plastic color -- olive or black -- and had little splashes of trim in red or brown, respectively, so they were kind of pre-painted) figures. Four of them, unfortunately, were molded in driver/operator sitting positions, so weren't really useful for miniatures unless you could put them in a vehicle. But they were cheap, and made great corporate security goons too. You might be able to find these at vintage stores, or garage sales, or eBay.
If you're looking for vehicles, surprise surprise, Hot Wheels makes a lot of 28mm scale figures. They may look a little small, but yeah, they're the same scale most miniatures are crafted in.