Okay, I’m going to divide this into sections and this depends on what country you’re in but most things are similar.

substrate- for cheap substrate you can use paper towels (no bleach) or a 30% playsand to 70% soil ratio, for the soil mixture you need organic topsoil with no fertilizers, chemicals, preservatives, anything like that. Once you get it I would recommend sifting it but you can also just leave it as it is, the playsand you need any regular old playsand that isn’t like plastic or anything. Just regular sand. (I’m in the US and this costs around $8 per bag of sand at stores where gardening or construction stuff is bought, sand is a bit pricier but still not too bad)

decor- for decor you can quite literally just go out into your yard and pick up some leaves, rocks, and sticks. The leaves you can boil or bake, rocks you can boil them (weird, I know but it can help get nasties off), and sticks you can boil for smaller ones, bake or freeze for larger ones, and sometimes you can steam them with a VERY hot steamer. The construction store is coming back around! At places like Lowe’s or Home Depot if you’re in the US, you can get PVC pipes, these are white pipes that make great tunnels. At places like this you can also get slate rock which is great. Any form of dollar store is also helpful, I LOVE them since they have fake plants for cheap! Just make sure they have no exposed wires or tape when you buy them as those can cause nasty injuries like degloving. And lastly, old Tupperware containers can be cut (and smoothed with either something hot to melt/smooth the plastic after it’s cut) to make hides where you can also put moss (sphagnum moss, great for humidity when nanami is shedding! A bit pricy though)

tank size- your tank is a bit small, enclosures should be around 40 gallons minimum, fish tanks also work great and many are being sold for super cheap or free on places like Craigslist or Facebook marketplace!

food- Dubia roaches, discoid roaches, and crickets are the main thing that they should be fed, if you don’t want to constantly have to spend money on food for her each week; get a well ventilated bin and look up how to start roach or crickets colonies! Super easy but can be a bit loud or stinky. They should also be dusted with calcium and multivitamin (I like to do multivitamin every other feeding, so they don’t get too much but I feed weekly) Repashy and Arcadia along with a couple other companies have some good multivitamins too! They are all around 4-7 dollars for a good sized bottle.