The betta "jars" in the photo are from stuffed animal collectors.They are pretty common in betta breeding as they are easy to see into.Also used are 1 quart deli containers.Not intended as long term homes,you want the bettas grown enough to sell at 3-4 months old.The small size makes daily waterchanges easier,which you need for fast growth and fin development.
Heres the diy rack in my fishroom.The rack is made of rain gutter,The drains are to the right side to allow semi auto water changing.