You can definitely use kegs without it being cold. Like Eelpout said, you will need longer lines. You could keep the keg in an ice bath. You can also find a cheap fridge on CL. Stick the CO2 tank and keg inside and buy plastic picnic taps.
I wouldn't say don't buy used but I would recommend checking out it first. When you are buying a used set up you are really looking at the unit itself (if it runs and if it is in good shape) and the CO2 tank with reg. Those are the most expensive parts. The lines, hardware and taps are cheap (unless you go Perlick but even then they aren't bad).
Primary: S'mores Stout
Kegged: Centennial Blonde, Dry Stout and Orange American Wheat