You could try Moca 2.0

300 ft is Moca 2.0 Max to get full speed just under 1000

[Link: amazon.com]

Per the specs the Max transmit is +52 dBmV and the Max attenuation it can overcome and still communicate full speed is 50 dB, for an input of +2 dBmv. It will still work beyond that but it will get slower.