Communicating between PICs over 30 feet
One option (assuming your desired device supports it... many Microchip PIC's do) is a CAN messaging system. It's extensively used in automobiles, e.g. so a tire rotation speed sensor and an accellerometer can communicate with the airbag computer. The protocol is designed such that you can have an unlimited number of devices communicating on one bus without collisions.

I use it at my company to communicate up to about 200 feet between a product and a controller. Highest standard baud rate is 1Mbit/s. It's fairly easy to implement in C. You'll need a CAN transceiver if you choose to do this; something like Microchip's MCP2551.

Here's the specification, here's pertinent app notes AN713 and AN754