I actually get asked this question a lot and my answer is pretty much the same each time: make a folding chair that doesn’t suck. The mechanisms are flimsy and the restrictions on things like what angle I can have the foot rest at is annoying (I like my legs at a 90 degree angle to the seat and folding chairs don’t allow that).
Unfortunately, I don’t think that fits within your $100 budget. In that case, I would focus on inventing a universal cupholder that can be easily removed and stored and is capable of handling everything from a thick pint glass to delicate stemware.
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