I would never consider paying for a show on a cruise. If it comes down to that, I'd just skip attending them altogether. I've been to so many over the years though, so there is just no wow factor anymore anyway. I must say, I do enjoy the theme shows the most, however.
I have walked out of a few shows because I thought they were so bad in years' past, so it would be laughable to think one might have to pay to see them IMO.