I've 4 515-8G in VG/Excellent condition (some might say 'near mint' but I won't).
Serial # stickers have all fallen off, but presumably they're from the same run/shipment as other components from the same units have proven to be.

A fellow enthusiast is interested in 2 or 4.
What's a fair price per driver?

All that I can find for comparison:

515-8g HP (Altec) (ferrite round magnet) recent months sold ebay: ~$250 ea (only one example found) (+$40 shipping)
515 "C" (Altec) (alnico) recent months sold ebay: ~$500 ea (+$55 shipping)
515-8C (GPA) (alnico): $1450 new

I'm on the fence as to whether I'd want to break up the quad, and whether it'd even be worth it to sell them.

thanks!