Another vote for a flat bar or even an endurance type road bike (more upright) here. I have back issues, but leaning forward a bit (rather than being completely upright and forcing my weight down on my back) completely eliminates back pain. I also noticed this when I was riding my Moto Guzzi V11 Sport with a bunch of buddies on Harleys...they had to stop every 45-60 minutes to soothe back pain...I could stay on a full tank of gas if desired. Try as many as you can and buy the one that suits you the best. Trek and Cannondale have some very nice fitness/hybrid models, but above your price point.