Hi,
is there any chance you'll offer some PLC device?
ON Semiconductor seems to offer a chip with reasonable price: http://www.onsemi.com/PowerSolutions/product.do?id=NCN49597
I'd just buy the commercial powerline to Ethernet converter boxes. Several vendors make them and they work at 100Mb. It is dangerous to work on these devices. Plus they need expensive UL type approvals.