LemonRX satellites are probably your cheapest option. The Spektrum Serial Quad Race Rx's are a great option but a little more expensive.
Connections are pretty simple, but depend on exactly which Rx you choose. There are only 3 wires (+, - and signal) - just make sure that you know what voltage is required - generally 5V or 3.3V. The signal wire will connect to a UART on the FC, the FC's manual will help you decide which one is preferable.