butterfly lever uperated up to which size 1

There is no standard answer to your question.

For centric BF valves for clean fluids the answer would be normal level operation for valves up to 150 to 200, perhaps 250mm for classes up to 150lb.

For some valve manufacturers the lower dimension valves would qualify also at 300lb. For this class the lever is used normally up 150 to 200mm.

Note: lever operation is in cases used for other, higher dimensions. Hand operated max torque have to be limited and be within the local rules. Max 20 Nm?? (Unsure figure). Anyway, if you have to use extensions for the lever you have chosen wrong.

Price difference: as for valves both levels and gears comes in a multitude of constructions and materials, and price difference will depend on each single solution, and need not be great or positive, even for smaller dimensions.

Safety of operation, precision and dependability, and not at least total cost over lifetime should weigh more than cheapest bying price. For double eccentric valves, and for other types of fluid, gear operation should normally be preferred for hand operated valves.

Thanks a lot for your help