Don't despair over riding a flat bar! I rode flat bar for ten years before getting my Look 566 road bike.
The Cannondale in my signature is that flat bar bike. She is basically the same as a "regular" road bike, just with flat bars. I rode several century tours on this bike. She has 700x23 tires, full Ultegra drive train and good quality road wheels. I ran clip on, tri style aero bar for a long time as well to help when the wind was strong or if I wanted to go a little faster. Not Bike Snob stylish, but who cares? This worked for me.
Check with your local library, they should have subscriptions to at least one bicycle focused magazine. Look through the back issues for information to help with your quest! Bicycling is a magazine that covers a wide variety of riding styles.
One piece of advice none of us has said yet. A bicycle store bike is almost ALWAYS upgradeable! When you find the one that works for you, you can always improve on the components, i.e. better wheels, tires, drive train etc. over time or as you want to spend the money.
Good luck and happy riding!