trying to get z77 with i5 3570k in ebay or even chinese website like taobao.com,they sell very cheap motherboard..
z77 for 45 usd,120bugs for i5 3570k.
I think you can buy another motherboard to do that, but I would said it doesn't worth it unless the board under 55 usd , if you can find one of the 945chipset board for cheap from ebay. I think that's better way to do.