American Airlines have round trip airfares travelling from Washington DC / Baltimore (BWI) to Kauai Hawaii (LIH) for $575, making 1 stop in Phoenix. This is a regular main cabin economy ticket.
Travel Availability:
Departs BWI: Jan 22, 23, 29, 30; Feb 5, 6, 12, 20, 26, 27
Returns: good availability returns on Tuesday, Wednesday, Thursday
Use dates and book it on Expedia , Orbitz or Priceline . Bundling hotel with airfare will save money.
h/t Flight Deal