They DO NOT need a bridge to work. The bridge more allows you functionality. You'd likely want the bridge if you wanted to add the bulbs to an automation sequence (turn bulbs on when you pull in the driveway, turn on/off at a certain time) or to adjust the brightness.
The starter kits are not necessarily cheap, but they do come with a bridge (make sure you buy the Hue Bridge 2.0). I think if you bought the starter kit and installed it, you would not look back.