Ghost shrimp would be a thing to try... cheaper and have almost 0 bioload
I got mine for 33 cents each, they live 2-3 years.... just watch out, they LOVE to jump out of tanks, and some bettas think they make better snacks then maids
Right out of the tank. :P They just keep jumping till they get to the top. My VT chased one right out of the tank and it died. :( They are cute little things though! ^.^ If you have a cover it's no prob. And be sure to get the biggest ghost shrimp at your store because, like LittleBettas said, some Bettas like to eat them.
Nerite snails don't reproduce, and just one of them the bioload isn't bad. Multiple snails or other species do poop a LOT. I have annoying snails that hitch-hiked from my plants that were cute at first, but not about 50 of them later... GAH. I bought a new, very large, plant, and within a couple hours it was covered in snail poop.
Ghost shrimp? Cute, fun to watch, and minimal bioload!