If you have a turbo trainer and a speed/cadence sensor, you can do power-based training using Trainerroad.com. You pay $10/mo and they have an incredible database of workouts and programs that use your bike's speed sensor to come up with virtual power. You just have to tell the software what turbo trainer you're using and they have a power curve that correlates rotational speed with instantaneous power. I have a stages power meter and a KurtKinetic Roadmachine. I have compared power with my power meter versus the 'virtual power' and they match very well such that I use virtual power for indoor training.

This is probably your best approach whether you do or do not have a power meter provided you don't mind indoor training.