"...Sam's Club for $29, and I'd just pack it over there as luggage"
With some airlines charging $25/each way, paying for one at home and checking it as luggage makes it more expensive that just buying one in Kaua'i at WalMart, K-Mart or Costco (Kauai has all three) and just abandoning it at the resort when you leave.
I wouldn't be surprised if that's where a lot of the rental beach chairs are acquired anyway.
Anyway from Yelp it appears that chairs might be fee at the Waiohai ->
http://www.yelp.com/biz/marriotts-waiohai-beach-club-kauai#hrid:w94kMvS0CGslPSn_xmzAcA
...Mark