Is there a good way to estimate the material cost of art made entirely of aluminum?

I use varying wire sizes, so I can't just measure out how much of one spool I used and measure the material cost in proportion to how much wire I used.

Should I just weigh the whole art piece and use the price of aluminum as a commodity, and not mind if I'm a few dollars off what my actual cost is? Or figure out roughly how much this wire costs by averaging the spool prices with their weight?

Pic related, spools on left and some aborted trial work on right.