You can find some good prices on road bikes all over if you looked for something used. But if your looking for something like a Trek, Speaclized, Cannondale, Bianchi, BMC... Any professional endorsed bike, even if it's a base model you'll be paying at least 700-800 dollors for it. I recommend something along the lines of a Schwinn's Fastback. Great Begginer bike for the money... Like these other guys said, Roadbikes can cost some serious money, I have close to $8,000 dollars invested in my bike. But I have been riding avidly for many years now. As for you ssprio I think cycling is a great form of cardio. Think of it in the same terms as running, like you would do HIIT, or prolonged periods of riding like they do on tours. Works the same way. But nothing can actually "replace" running in my opinion.