At the price stated, I don't think you will get a lot of value from older higher end phones as midrange chipsets now + the cameras in midrange phones are often on par with and in some cases better than stuff 3/4 gens back (which is not that long ago). For instance, the xiaomi redmi note 4 outperforms my galaxy s5 in terms of camera performance, a working fingerprint scanner and is on par with it, if not better than it, in day to day operations (though the ui slowdowns might just be its age showing). If you get a good deal on second hand flagship, you can use your judgement and buy it if it looks like a good, but I'll just highlight some midrangers you can buy new.
If you're on android and are looking for qualcomm based chips, you'll likely have to limit yourself to the snapdragon 400s, and at most a snapdragon 625. There's probably offerings from mediatek but I don't know much about that chipset. At this price you can expect to be able to do most things just fine, stutters might be noticeable sometimes, but nothing completely unusable (I've used a 40$ phone for 3 months while my regular was getting fixed and while it was hardly optimal performance, it got the job done. [Phone gets slower when it comes to the internet, but offline things work just fine. Camera was slow/bad as expected.])
In terms of availability, I assume motorolla is more readily available than Xiaomi or Honor (by Huawei), though the latter two have more bang for the buck in general, so I'll start with that. The moto e4 and especially the plus are great phones at this price. They'll stand up to standard usage just fine, has a decent camera for the price as well as a fingerprint scanner. The standard e4 has a mediatek processor while the plus runs a snapdragon 427. Now if you don't mind third part skins that is reminiscent of ios and have xiaomi phones available, take a look at the xiaomi redmi 4x and the redmi note 4. They have class leading build quality, camera performance and chipsets in this price range. The note 4 has the 625 which is a bargain at this price range (the g5 plus faint suggested uses this chipset and costs 200$ more) and will improve the phone's usability by quite a bit, even handling 3d games decently while the redmi 4x has a 435 which will have better/similar performance as the moto e4 plus. They also have much bigger batteries.
My recommendation would be the note 4 if you can get it in your price range, which you should be able to according to gearbest (
1 &
2) if not, its a tossup between the motos and the 4x (Try to get the e4 plus). I wasn't able to get a solid idea about the e4's price but the regular e4 should be at least in your price range and the 4x is definitely in your price range. Also, it seems you can get the moto for even cheaper with some amazon prime deal where you get ads on your home screen ->
so you can look into that as well.
If you want more options, there's this channel that reviews rando chinese phones in terms of price to performance so you can check him out.
https://www.youtube.com/channel/UCX3l3PzU1hIbsQKauQefh3g/videos . You can also find out about cheap phone options from unbox therapy but that dude's unbearable and he doesn't really do reviews - more like a drawn out unfunny first impressions. You can just search up any phone that interests you in his channel and find out more about it.
Hope this helped somewhat. Also, see if it's possible to raise the budget to like 200 USD because you can more comfortably get better phones at that price. For example, the honor 7x is 200 and has gotten a lot of praise from the tech community (for good reason!).
edit: if you don't care about fingerprint scanners, xiaomi also has the redmi 5a which is sub 100$.
