We use a POS system called WiNRETAIL by a company called JDS Solutions. Can you get this point of sale system integrated with Bigcommerce?
We have not worked with WiNRETAIL before looking at their website they appear to have a nice solution for independent retailers. I couldn't find an application programming interface (API) listed on their website but they did list some nice import/export features.
If you can get us in contact with the folks at WiNRETAIL I'm our engineers together can figure out a way to automate the importing/exporting of data for you to completely automate the integration with Bigcommerce for you.
Please Contact Us when you're ready for us to talk to WiNRETAIL and we'll get our engineers talking with their engineers and we'll get this figured out for you. We have a bunch of ways to integrate with 3rd party systems and I'm sure we can figure it out. Thank you.