What's the best/inexpensive way to get image or etch mason jar?

My son's bday is coming up and I'd like to have 50 mason jars as glasses and for guests to take home as a favor. I want to do this for as little money as possible. I thought if I could etch them or even transfer an image that would work, but I'm having a hard time finding anything. If I transferred the image I'd want it to be obviously washable. Etching seems like it may be too hard unless I'm missing something. There are reusable stencils, but I can't imagine having to make 50 mason jars with 1 reusable stencil, that'd take forever. I'm trying to do it for as cheap as possible :) Any ideas?
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