I ordered my terrarium from Amazon. (Petco has stuff too). A company called Exo-Terra makes really nice ones. It literally comes with everything you need (except for the light bulb, and possibly a heating mat depending on the temperature of your house.)
You can really use almost any type of aquarium and put a screen over top and save some money but I wanted mine to look nice so I got this one:
http://www.amazon.com/Exo-Terra-Lanka-Rainforest-Terrarium/dp/B004OHPTEC/ref=sr_1_fkmr0_1?ie=UTF8&qid=1329980645&sr=8-1-fkmr0
Again though as long as you have a tank, a lamp, and screen to go over the tank (since they need ventilation) you can house them. Of course there is substrate too which is usually coconut fiber and runs about $3 - $4 a brick. I only used one brick and had a bunch left over.
To keep it humid I did a mixture of things, Its cool in my apartment so I bought an under tank heater (the Rainforest Heatwave by exoterra, its the only one I found that is safe for frog tanks) and I spritz water in their tank two to three times per day.
They really are awesome little guys, I highly recommend getting them. http://www.floridaherps.com had the best prices I found and you can order babies or adults.
Their food is dirt cheap, simply buy crickets for roughly 14 cents per bag which should last a week easy with 2 or 3 frogs.
ok so the most expensive thing is probably the terrarium I guess ill go to petco and ask some questions and stuff but you pretty much answered everything....