If you truly 20 qual every red map you run, you'll run out. At one point I think I stockpiled 400 and started using them (only on white maps) and ran out. It does seem you average somewhere between 1-3 per map with the current league mechanics though and if you're targeting it or speccing for it you could surely get 4+ per.
Looking at scarab prices for just rusted, top end are 5c, then 3,2, 1, 1, then everything is 0.5c each. Polished aren't much more. I can't imagine unless you're selling them by the 10's it'd be worth it unless you're really hard up for chaos. With scarabs being shit out nonstop from Eater mods I definitely expect prices to fall as low as possible for them with only one or two league scarabs holding value due to cheese synergy with Atlas shit.
Speaking of: certain very cheap scarabs such as Abyss and Metamorph paired with Atlas passives are massive free money. Essentially you're put a 2c+ mod on your map for 0.5c each and with the double metamorph rewards or the +3 Abyss/6 affix Abyss stuff you're bound to luck into some major money. An 86 stygian vise is like 5c+ for just the base and that's almost guaranteed with the passives for Liches. Pair that with slamming it with nearly any resist/life/attack harvest and you can roll a 2-3 ex belt very quickly.
Once again there's going to be more money in running your shit if done correctly than quick selling, but for a lot of it like Bestiary or Torment I can fully understand just offloading them 20 at a time for an easy 10c sale every 5 maps.
