Looking further at the Axiom 8051 board set:

They have a 4x20 character LCD module for $35 and a 4x4 keypad for $25.

The nice thing I hadn't noticed before is that they have an EPROM with a monitor and BASIC installed and your program would be loaded in a 32K bytewide parallel EEPROM to easy changing. It has 32K of external RAM too. The only thing I saw missing was a RTC. Using something like this could reduce your hardware costs significantly and reduce the size of your case.

Having the code in bytewide EEPROM suggests that you might be able to right some self modifying code to make it even harder for them to copy your code design.

I'll think about some algorithms.

aka J