The big divide in road bikes is - do you want to go for a bike ride, or do you want to work on your fitness?

The former can be done with a broad selection of road bikes new and used at all quality levels. Sure, go get that $350 Craigslist bike. As long as it's in good running order you can go as fast and far as your muscles want to.

The latter sort of pushes you to more expensive and recent bikes, because you are going to add a GPS head unit that guides you through programmed workouts, a power meter to go with that, heart rate and maybe speed and cadence sensors, a trainer to do Zwift, etc. And since all that works with your personal electronics and the Internet, there's a constant drum beat to keep it all up to date.