But the customer still owes me a little money, and I won't get started until he liquidates...

I've got a similar situation, on a project for my former employer (the place I retired from): no more work until I see some green. I'm unlikely to see any green from them until they see some green from the end customer, and since the end customer is the gummint that could take a LONG time.

Which is frustrating, as this particular project is one I'm very enthusiastic about; but my enthusiasm has its limits when it comes to working for free.

 

... but my enthusiasm has its limits when it comes to working for free.

Right back at ya... that's something that I had to learn through harsh experience...

 

Arduino has server software and ethernet/wifi support: http://playground.arduino.cc/Main/InterfacingWithHardware