Well, with the resevoir... Do you need to buy from them? Could you not potentially get a small rubbermaid?
You can use anything that will hold water with a flat surface into which you can drill a 5/8" hole: an aquarium, Rubbermaid container, bathtub, etc. Those big Rubbermaids are pretty tough. We recently used three of them to hold gasoline while my mechanic buddy and I drained my completely full gas tank to swap out a fuel pump seal. (Certainly not a good nor safe idea, but better than dumping it on the ground.) They were pretty unwieldy when that full of liquid, though! We looked around for someone with a video camera in the bushes, just in case.
I'm like everyone else; I don't like paying out the wazoo for something that I can get myself, so I thought it would be cheesy to sell a $5 Home Depot bucket online. Unfortunately, that reservoir is expensive because it's made for food service use, so I only make about $5 on it. It's more of a "convenience" item, plus it's slightly smaller than a five gallon bucket so it doesn't take up as much room.
Whatever you do, try to use something that's translucent! Having to lift the lid to check your water level turns into a PITA after you do it a couple hundred times.
Plus. What about a fish pump?
If you find a cheap one that works, let me know! Fish pumps are made for water circulation. A good misting pump needs to not mind having its output severely restricted while maintaining a fairly high pressure. To get an idea about the difference in required force, set an adjustable spray bottle on "stream", then increase it to a finer and finer mist. An aquarium pump is about the equivalent of the "stream" setting, so it won't work with real misting nozzles.
Anyway, regardless of where or from whom you buy it, get a
good misting system if you choose to buy one. Don't be tempted by the HabbaMist. It's money better put towards a real system (spoken as a cham keeper with a HabbaMist in the closet).