Bulk smoke alarms — who's got the best source?

Every property burns through smoke and CO alarms — replacements, expirations, turn stock. Prices per unit swing wildly by supplier and by sealed-battery versus hardwired. Share your source and your per-unit cost, and what shelf life you are seeing on the date codes when they arrive.

Since this is the trade board, I will set the ground rule: share sources and prices freely, but check the date codes when the boxes land. A cheap alarm that arrives with three years of its life already gone is not cheap. Sealed ten-year units changed the math for a lot of us — more per unit, far fewer battery calls. Where are you buying alarms in bulk right now, and what is the per-unit price looking like?