So you have three IR sites.
You'll need the following equipment to "properly" connect the sites together.
TeNSR channel bank at each site with 4 wire E&M cards, SRU cards, and WAN card. The analog audio connects to the 4 wire cards and the Astro audio connects to the SRU cards. This is assuming you have v.24 wireline boards in the stations. Also a serial 9600 baud connection is needed from one of the Quantars to the SRU card. A T1 circuit will be needed to go from the channel bank to your master site.
You will also need a SmartZone master site which will require an Embassy switch, at least one zone controller, user configuration server, and zone database server. It would require a network manager workstation also (to edit zone database and user database).
This would be the minimum equipment to connect the sites in a Motorola supported fashion. There is other equipment I've left out (routers, switches, ATR server, FullVision).
Last, your subscribers must be flashed and programmed for SmartZone operation. Depending on the size of the fleet this may be a huge undertaking.
I've left equipment off the list such as routers, switches, ATR, FullVision, MOSCAD. etc. The bottom line is this is a HUGE job and needs to be properly engineered.
Some people may have suggestions on alternate methods of connecting the IR sites but the proper way would allow seamless roaming between sites. I can't even guess at the price to do the above properly but I would think at least $1 million.