We did a Luau in Maui thru the NCL Star back in 2002, $90 or more per person. It was NOT worth it. Too crowded, over 500 ppl and you could barely get to the buffet much less see the show. Unless they have improved it, do it on your own. I heard Old Lahaina is the best in Maui. http://www.oldlahainaluau.com/index_main.html
Or do one before or after your cruise. We found out when we docked back in Waikiki, we could have done it for $45pp thru the hotel.