To keep my Phalaenopsis gigantea seedling warmer in winter I set this up. It's a large vase covered with plastic wrap, held with a rubber band. The bathroom tiles are 4" / 10cm squares.
There is a layer of LECA at the bottom, then the pot is sitting on top of a jar with some water. The base of the pot is not in the water. I considered having water at the bottom of the vase but decided not to so I wouldn't need to clean out the algae.
The vase sits on an electric reptile heat mat, which sits on top of the lid of a polystyrene foam cooler.
I keep my eye out for suitable terrariums. This is from Marshalls, a discount store in the US. It cost about $6. They often have very large glass vases or storage containers for little money. I also frequent second hand stores and yard sales for large vases and old aquariums. I have plenty of each at the moment.
A food, kitchen and household market in the US called Smart & Final carries Anchor Hocking 1-gallon lidded glass food storage containers for about $15. These make great terrariums. They would hold a medium-sized Phal or a number of smaller orchids. They also sell 2-gallon lidded glass beverage jugs, which could be used as well.
You can get foam cooler boxes of various sizes if you know somebody who works in an operating room. Or, at the office of a physician who does cosmetic filler or Botox injections. Supplies are shipped on dry ice in thick foam coolers, which are thrown away after one use. If you ask they will be happy to give them to you. They are much better insulated than expensive coolers sold in the US by companies like Coleman. Stores selling tropical fish also have very large foam coolers, in which the fish are shipped. I recommend keeping them in the cardboard box for better support, and to protect the easily-damaged foam walls of the cooler.