It's worth distinguishing between two completely different types of "servos": RC hobby servos, and industrial-type servos which are robustly built like steppers but significantly more fast, accurate, efficient, and powerful. They are hard to find in Nema 14/17 sizes but not impossible.

RC servos typically have an analog or PWM signal interface. That would usually not be accurate enough for an industrial servo in positioning mode. Industrial servos, like steppers, have a digital interface which might be a serial format or STEP/DIR pulse train. Some drives will accept a -10V to +10V analog signal for velocity or torque control mode.

Anyway, here are some Nema 14/17-sized industrial servos with online pricing, which might be what you're looking for?

https://en.nanotec.com/products/2262-smart-servos-motors-wit...

https://catalog.orientalmotor.com/viewitems/l-categories-ser...

Or many companies offer stepper motors with built-in encoders and controllers to prevent missed steps:

https://catalog.orientalmotor.com/viewitems/az-series-absolu...

https://www.zaber.com/products/stepper-motors/X-NMS-E