If you are using CR123s, then cost of operation is very obviously a low priority to begin with. Might as well be safe and use something decent. Even the RayoVac brand of CR123s have a great track record and can be found under $1.50 per cell.
If you are really looking for a way to reduce your cost of operation on a light that is used frequently, the way to do that is by finding an appropriate rechargeable solution for the light in question- that can often be BACKED UP by CR123s (in many configurations and lights).
li-ion cells have a good track record of safety here, arguably much better than CR123 primary cells. If you use your light enough, the cost of a nice charger, and some cells, can overcome the cost of using CR123s within weeks or months depending on your usage patterns. Also, when you know the cells being used can be recharged, you are more likely to use the light when you may have otherwise "saved" it for fear of burning through expensive CR123s.
If you are interested in a rechargeable solution to your light, give us some information to work with about which flashlight you need to make rechargeable. Some are better candidates than others.
If you prefer to stick with CR123s, (perfectly understandable), then please, spend a little extra and stick to quality cells.
Eric
