Not sure where you are located, but around here the single speed craze is big. Most single speeds are repurposed old road bikes. Most have hand brakes or are fixed. Fixed would probably not be what you want either. BUT thinking a coaster brake on an old road bike would give you a lighter option than a cruiser. It would be much lighter and more nimble and not terribly expensive.
Best of luck. And have fun looking at your options.
S