You want to start & stop a conveyor?

how many times per minute?

How much does the conveyor weigh?

How accurate does the positioning need to be?

if you want to implement a genova mechanism type it will come out more expensive then stepper motor. i think you should consider a continous drive (AC motor) and control the position in some other way.

as i don't know what's the application i can't suggest any specific mechanical solution.

You explanation is difficult to understand, please take another shot at explaining, make only short sentences....

As requested by Andy, can you supply more information or a new description?

I would suggest though that if stepper motor is not affordable, then next most reliable would be a continuous running motor and electric clutch with a timer on the clutch.