Don't break the bank with a carbon bike. There's tons of road bikes out there that will do the job for someone new. I've had a diamondback expert for the last 5 years and have put maybe 5,000 miles on it, most of mileage in the last year and a half. If you're in a hilly area go with a 27-speed (triple chainring up front, 9 cogs in the back). That's about it, find a bike THAT FITS and just ride. I'd be weary of anything under $400(only because the components CAN'T be good at a price like that), but wouldn't touch anything over $1,500(incase you find out that you don't love road riding and now you have a sick bike but won't ride it, of course the resale can be pretty good if it's a SICK bike). My $1,000 road bike has done me great over the last 5 years and only now am I thinking of getting an actual road racing bike.
Oh and clipless shoes/pedals are really important if you want to log tons of miles. Overall depending on what you do you could spend as little as $600 or as much as $2600.