At that speed, and if you won't need fancy buffering and got the necessary 3.3-ish volt ready, check out some esp8266-based mesh/repeated tech. Possibly with us

At that speed, and if you won't need fancy buffering and got the necessary 3.3-ish volt ready, check out some esp8266-based mesh/repeated tech. Possibly with using wires on their (quad-) SPI bus to pair two, potentially over quite a sizable line length. Saves airtime.