>>6007016Revoltech Gyaos is pretty good for such purposes.
For a larger monster, there's Diablo from Diablo 3. I'm not sure what's the pricing on that piece now but it wasn't that expensive when it came out.
Some of the villains from Figuarts work. Hell, some of the heroes from SIC work too. I have SIC KT as my monster race. And if we're talking Figuarts, we might as well talk Monsterarts.
Some vinyl kaiju work as well. Of course, a lot of them are probably too silly to fit in but there's a few that fit in pretty well. It depends on how articulated you need your monsters to be. If nigh-statues work, I think Ben10 actually came out with a few "realistic" staction figures a few years back too.
Berserk Garo's great if you can find him in decent condition for non-rape prices. I just ordered that new-ish "Garo goes rabid" form precisely to pit against my 1:18ths.
Personally, I'm using MSIA and Revoltech as the robot apocalypse for my Joes. Even some TFs work for that setting.