As far as humidity, you can usually get a small room sized humidifier for cheapish that will work better than the humidity trays. Of course if you just have a few, it's not worth the investment but after 5 or so, it might be.
As far as most box stores you can actually talk them down on prices on orchids. I usually walk out with them at no less than 50% off. It doesn't hurt to ask, you might be surprised at what they say. Plus, make friends with the garden manager.