United is currently having reduced saver awards in Economy to Hawaii from US and Canada for a limited time. The normal cost for a saver award in Economy to Hawaii is 22.5k miles one way as noted in the award chart below. So a roundtrip will cost you 45k miles.
However, you can currently get to Hawaii for 36k United miles roundtrip. There are restrictions though. You must book your travel by April 19, 2015 and you must travel from April 14- May 19, 2015. It must be a roundtrip flight and these reduced miles are also only valid Monday -Thursday, so no weekend travel. Open jaw is permitted but stopovers are not.
I did a quick search of saver award availability in economy from New York (JFK) to Maui (OGG) and found some pretty good availability. Please note that Premier Members and members with a United MileagePlus credit card see more award availability. So if you see less availability, then this is the reason.
JFK-OGG
OGG-JFK
I also did a search from Houston (IAH) to Maui (OGG) and also saw great availability.
IAH-OGG
OGG-IAH
So if you are thinking of going to Hawaii soon and have a stash of United miles waiting to be used, then this would be a better time to use them.