I agree with Niles. I would have them balanced for peace of mind. If you end up with any vibrations when the car is finished and you don't have them balanced, this will nag you to no end until you finally take them back off and have them sent out for balancing. At that point (in time and money) the cost will be more than $80
. Plus, if they don't require balancing, the shop should tell you so and the cost won't be the full $40 per shaft since they don't have to weld on any weights and recheck the balance.