You will need a local-wireless network to access the internet or to access your store's PC/server. You can utilize bluetooth; but, I find it very unreliable more than 40 feet away. You can buy an unlocked cellphone on Ebay that has the barcode scanning capabilities and that you will not have to use a service to utilize.
Just borrow a wireless router and set up a home/business network. Once you have it established; set up your remote device to connect to this network via the network's settings(name, SID, etc.).
Check out this website for some great products. I used to utilize many of their RFID products back in the day.
To me; it sounds like you need a mobile inventory device/system that incorporates your current system.
I hope this helps...