How long is the distance between each PIC?
If you have 3 or more PICs one idea could be a looped bus. each PIC has one receiver and one transmitter. PIC1 TX to PIC2 RX, PIC2 TX to PIC3 RX, and PIC3 TX to PIC1 RX. If the normal condition is that all (RX) are connected to (TX) inside the busdriver, and it is possible for each PIC to transmit separately, you can make a very fast, and secure bus. All PICs are listening all the time, and when one transmit a message, it will normally see the same message at its own input, and discard it. If two PICs start transmitting at the same time the messages will be received and retransmitted if not from itself. This way the max latency is 3 messages, for 3 PICx transmitting at exactly the same time.
If you want to have no collisions you may run the data through the PIC, but then you will have a small delay for each PIC in the loop.
You may also use a token based communication. Having a token running around and the loop, and the PICs connecting messages on the token, and picking their own messages off the token when it comes around.
All this my be realised with mostly any type of point to point drivers, like pure logic, RS232, RS422 and so on. All depending on the distance to communicate over,
One thing to be aware of is that using RS485 multidrop comunication without a master slave solution is not adviceable. It is not possible to detect direct colisions from two masters, reading the sent data from the sender side. You then have to make this a security feature in the protocol used.