A breeding net is usually used for live bearers to protect the young from being eaten. They shouldn't cost more than $4, but I'm not sure exactly how much they cost. You should be able to find them at your local fish store. Here's a picture of a breeding box, but a breeding net is pretty much the same thing only a free hanging net with floaters at the top.
Breeding box

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Phishie

"An ounce of prevention is worth a pound of cure."