The cheapest would probably be: get a 'regular' bookPC and replace the cd-rom with a cheap DVD drive. That would be approx. $170 + $53 = $223 (which is cheaper than the $289 they want for the DVD-BookPC).
I did see a guy selling BookPC's on eBay a while back that had no cd-roms for about $125.
The bookPC has no serial port. A usb-to-serial adapter may or may not work with a serial shut down controller.