Seems like a relatively good deal. I needed one; one left. Seller accepted $300 best offer.
Supermicro BPN-SAS3-846EL1 4u 24 Bay SAS3 SAS2 SATA3 Expander Backplane | eBay
Supermicro BPN-SAS3-846EL1 4u 24 Bay SAS3 SAS2 SATA3 Expander Backplane | eBay