I know using a Vex as a co-proc would be cool and all, but I think it's wayyy overkill. You can get a top of the line
AVR ATMega2561 (pdf warning) for a mere 10% of the price of a vex controller ($16.99 at Digikey). Lets compare the specs.
Vex:
- Chip: Microchip PICmicro® PIC18F8520
- Speed: 10 MIPS
- I/O: 16 10 bit ADC
- Program space: 32Kb
- Programming language: PIC C (Not totally ANSI)
AVR:
- Chip: AVR ATMega2561
- Speed: 16 MIPS at 16MHz
- I/O: 16 channel 10 bit ADC, total of 86 programmable IO lines
- Program space: 256Kb
- Programming language: avr-gcc (AFAIK ANSI)
AVRs have the advantage in every category. Spending an extra $130 to get a fraction of the benefits... nah.