I'm guessing that the welding wire you are referring to is for TIG welding. It can be had at any local welding supply house and usually comes in a one pound box with each wire being 36" long.
Shouldn't be much more than $10.00+/- and it would be enough for a thousand SPADS If you're getting steel rod, then get 70 series (70,000psi tensile strength when used for welding)
I'm going to build my first spad real soon to further enhance my fleet and to turn a few heads at the field. Great Forum