this really belongs on the Invertebrae forum, but what the heck
I know a few places you can get mantis egg sacks (called ootheca) they are so fun, and easy! Check around with gardening/farming stores, they sell them as a natural pest control (to eat all the aphids/grasshoppers, etc.) and you can get them for like $5-$10 each, and you can hatch like 300 babies from one, put them in a big cage, and feed them on store-bought fruit flies, or just let them eat each other, and they can eat small crickets within 2-3 weeks... Not very good to keep more than one together, but a large tank might hold a couple, if they are well fed... I have a caresheet I wrote, if you want to see.
Dan Conner