I go to Kauai at least once a year and there are several great ukulele stores. I certainly would not buy an uke in a gift shop. My favourite store is Scotty's across from WalMart in Lihue, who has the biggest selection, but the price you negotiate really depends on the day and his mood. In Hanalei Bay, there is a store called Strings&Things or something like that which has knitting supplies and Ukuleles. Both stores carry ukes made by the main uke builder on the island, Raymond Rapozo (Island Ukulele). They are gorgeous Koa instruments with an open pore finish and they sound great, but are a bit overpriced for me. They have a label that looks like this:
The uke in the picture looks way too glossy, and I am not aware of the brand/builder displayed on the label.