Fortunately Mantids do not need elaborate housing and will do as well in nothing more than a plastic sweet jar or pint pot. Ideally the height should be at least 3 times the size of your Mantis. Some form of netting, tights, voile or just kitchen roll can cover the top and can be held in place using an elastic band. A small feeding hole can be made somewhere in the jar or the top of the netting just big enough to push food through and can be bunged with a piece of sponge. A small twig stood at an angel for climbing can be added but make sure it doesn't hinder the Mantis when it moults, a mantis needs to hang without any interference. Also a piece of kitchen roll placed from the top to bottom will provide an additional place to moult and enable non flying live food to climb.
Substrate is optional but humidity is essential in many species to aid moulting and can be achieved by lightly spraying the housing 2 - 3 times a week, check on your species requirements.
Below is a simple guide for making a cheap and effective mantis enclosure.
Firstly you will need a clean plastic pint or half pint pot depending on how big your mantids are, remember that they will need enough room so that they can hang and moult without difficulty.
Melt a feeding hole in the pot using a soldering iron, use one with a rounded point. I pefer to do this near the bottom but allow enough room for any substrate that you might use. Make the hole slightly larger than an aquarium airline pipe.
Cut a small piece of sponge larger than the hole so it fits the hole snuggly and tight enough to stop any feeders escaping. The hole can also be used to moisten the substrate.
Cut a piece of fabric mesh, net curtain or even kitchen towel to cover the top of the pot, this needs to be fine enough to so that fruit flies cant pass through and secure it over the top using an elastic band.
Thats about it, just add substrate if you wish and a stick, remember to place it at an angle so not to hinder moulting.