but the the AVR-CAN is about the same price as a sparkfun CAN-BUS shield by itself (without the Arduino).
It appears there are multiple devices going by "AVR-CAN", and it's not clear which one we're talking about.
Olimex is $39 euro.
http://www.olimex.com/dev/avr-can.html
Sparkfun is $53
http://www.sparkfun.com/products/8279
SK Pang $34 Euro (same as olimex?)
http://www.skpang.co.uk/catalog/avrcan-at90can128-development-board-p-292.html
Here's a raw header board for $30:
http://www.sparkfun.com/products/655
Any of these, if it can do what we need, is cheaper than Arduino UNO ($30) + CAN Shield ($45).
There are advantages to the AT90CAN128: Internal CANBus is a big plus, since you don't have to interface to the Microchip parts. Probably lower overhead and cpu-loading as well.
Arduino uses the ATmega328, with 32K flash and 2K SRAM, 1K EEPROM is less potent than the AT90CAN part, if code size becomes an issue. (128k-bit flash, 4k RAM, and 4k EEPROM)
The advantages to the Arduino+Shield combo are the microSD slot, GPS header, joystick, and existing software (both Arduino itself, and the CANbus example code)
I put a lot of value in the microSD slot, since that's a ready-to-go logging solution right there. No laptop required. Between a 4x20 serial LCD display that just plugs in with three wires:
http://www.sparkfun.com/products/9568
, an enclosed microSD, and NMEA GPS input, I'm thinking it's a good place to start.
If someone wants to productize something, the AT90CAN128 is an obvious choice for a custom board. That would rock.. add a 4-bit LCD interface (cheaper than serial), microSD, some input buttons, GPS header. If you wanted more than one CAN interface, then you're back to the Microchip solutions. It does have 2 UARTs.