That's one way to go. You'd wire up your network like Figure 25
and only 1 device can be transmitting at a time. (half duplex)
The chip itsef is less if you have a way to wire them up yourself
http://uk.farnell.com/maxim-integrated-products/max488ecpa/ic-rs422-rs485-txrx-250kbps-5-25v/dp/2071314
"connect a power supply to the prominis and only have the master connected to a computer"
That would certainly work fine. No PC/USB is needed for the slaves.