When we need extra nights, we stay at the Aqua Kauai Beach Resort Hotel. It is ocean front, 10 min. from the airport, and has a free shuttle:
http://www.aquaresorts.com/hotels/aqua-kauai-beach-resort/
The units are studios with a wet bar with mini-fridge - fine for 3 nights, and they have restaurants on-site, including an inexpensive pool bar and grill.