Single, party, beaches, women, cheap...
Banana Bungalow Maui...
Its the best party hostel I have stayed at, and quite clean. Also did I mention the large abundance of European women?... Its not close to a beach, a 20 minute bus ride. But its a great party atmosphere.
I will also suggest
Rio Guest House Barbados. I went three times in 2011. Its right across the street from an amazing beach, warmest water I have ever swam in. Its also located in "The Gap" which is where all the bars are. You find mostly British vacationers, in turn very good looking women. Its incredibly cheap, clean, basic accommodation. $5 American for 6 pack of good Banks beer.
Those would be my two suggestions for cheap, and going alone.
But you can't really go wrong anywhere, if there is a beach, and hostel.
I would avoid the all inclusive though. Boring as a single young guy. Hostels is where the fun happens.