Those Porlex knock-offs are not very good, IMO. 8 dollar grinders being rebranded and sold for triple its worth on Amazon. The cheapest grinder I would recommend would be the Hario Skerton, which has its flaws but will do medium/ med. fine well enough.
Something like the Aergrind would be a definite step up for portability at least. Comandante looks good beyond that. I currently own a Kinu, which I'll be the first to admit is not worth the money, but in general you do get what you pay for.