It depends on what you shoot.
assuming you thought ahead and stocked up on PRIMERS.....
HA!! Voice of experience??
More than once ! It will never happen again though !
you need to look for deals and buy supplies in bulk. Buying a 100 primers or bullets at a time won't save you much. But buying 5000 primers and 3500 bullets at a time will.
Many choose to reload for many different reasons...
Cost savings seems to be one of the more common reasons I hear. Like already said, there are many variables with this one.
Produce higher quality ammo.
Many actually enjoy it and view it as an actual hobby itself.
Gets you through times of ammo shortages, assuming you thought ahead and stocked up on PRIMERS.....