Hi Jadeco!
I think every college student needs orchids, so I'm glad you have a few. That's enough to get you through the tough studies/exams. They will keep you sane. Orchids have a way of doing that. They definitely try your patience, but they keep you sane.
What I would do is kindly ask your Grandmother to replace her humidity trays because they are out-dated, and then offer to take her old ones off her hands.
Actually you can find make-shift trays here and there at lawn sales, Walmarts, etc. Ice cube trays work, depending on the size of your pots. Let your imagination run wild.
What's your major? Did your Grandmother get you excited about orchids? I think that's wonderful that you have an interest in orchids and I wish you all the best in your studies. If you have any questions, give us a holler.