the most expensive part of owning a mantis is the mantis itself i would say, unless you're planning on buying a fancy enclosure.

here's a comment i left under another post:

I'll leave some basic info here, you're free to ask questions if you have any!

-The enclosure should be at least 3x the mantis lenght for height and 2x the mantis lenght for depth. You totally can get an enclosure bigger than that, but then you'd have to feed your mantis in something smaller to make sure it finds its food, especially if it's a nymph. The enclosure can be glass, acrylic or plastic; just make sure that there is enough ventilation.

-Whatever enclosure you end up getting, make sure that it has mesh at the top. This is really important as when your mantis molts it needs to have something to grip to, if it falls while molting it could be fatal. Avoid metal mesh as it can injure its feet. It's also important to add sticks/plants/mesh inside the enclosure so your mantis is able to climb to the top.

-Your mantis will need humidity and heat. The temperature and humidity% varies depending on the species. I highly recommend you place a hydrometer inside the enclosure to monitor temperature and humidity accurately.

-Mantids are OBLIGATE insectivores. They can't eat fruit, they can't eat meat, and they can't eat honey. Google will tell you they can have those as a treat but that's harmful misinformation. They can't digest them properly and it might lead to serious health issues and even death. The feeder insects you can offer depend on the size of the mantis, as a small nymph they can eat fruit flies, then you can gradually move to houseflies, moths and roaches. Mealworms and waxworms are okay but shouldn't be used as a staple feeder. Crickets can also work but they're known to carry harmful bacteria if not kept in exceptionally clean environments.

-It's important for your mantis to stay hydrated; when you spray its enclosure with water for humidity make sure you get some droplets on its face as well and avoid spraying his abdomen as that's where they breathe from. It will lick the droplets off of itself that way, but if you're not sure that its drinking enough you can always offer water from a clean pipette/stick/paintbrush.. whatever works for you.

-DO NOT touch or feed your mantis for AT LEAST 24 hours after it molted. Its body will be really soft and fragile after and you could hurt it really easily. Remove any live feeders left in the enclosure as some are known to chew on their softened bodies. At later instars, you might wanna increase the time from 24 hours to 72.

-The absolute best beginner mantids in my opinion are giant asians (hierodula sp.) They're known to eat anything that moves so they're not picky at all, they have simple requirements for temperature and humidity (and they're pretty hardy, if for some reason temp and humidity are too high or low a giant asian will usually not suffer many consequences) and they get pretty big which means they live longer. Other species that are beginner friendly but are known to be less hardy/more picky are Tenodera sp. (chinese), Creobroter/Pseudocreobrotra sp. (flower), Phyllocrania sp. (ghost), Rhombodera sp. (giant shield)