Cheap spokes. I see decent prices on Ebay frequently. Of course, my idea of inexpensive might not be the same as any else's. For example, at a local bicycle shop, the stainless steel butted spokes set me back $151.00 CND plus 15% sales tax....
The spokes on this set of wheels set me back $0.00...
Years ago, as I harvested parts from bikes, for different reasons, I started saving spokes. Stainless steel spokes, straight gauge, butted and double butted. To be saved, the spokes had to be taken from a little used wheel and neither the wheel or the spokes could show any damage.