After searching around, I found a PCI-e dual ATSC tuner that has a Linux driver (not sure how reliable). The prices are as of October 30, 2009.
Case: Apex MI-008 ($39.99) – 250W is a bit overkill. I doubt this system will use more than 60W.
Motherboard: Pegatron IPX7A-ION 330 ($149.00) – the same as [...]