You can have lots of sensors reporting back to the central unit. The limitation is really the location of the central unit in relation to the sensors but they have a lot of range. Early on I did a posh school down here with 15 temperature sensors in the class rooms and 15 current sensors on the A/C units and 15 Lux sensors on the lights. One central unit coped with all of that. I don't think your shop is going to stress the limitations.
Pricing I am not across, it's another branch in another suburb, but it is going to be dependant on what you want. PM me with the gear you want to monitor and I can have a chat with them if you like. What they are selling here is access to the information gathered and the reporting of error states. The gear itself is quite cheap but it's the ongoing costs, the monthly access fee, that you'll have to consider against the risk and cost of losing your stock again.