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 POV ION330, has a 16x PCI-e and nVidia ION (GeForce 9400M) can enable Blu-ray playback. There seems to be a linux driver (look at the second and third messages).
  
• Tuner: Hauppauge WinTV-DVR-2250 ($99.94) – Dual ATSC tuner with Linux support.
  
• Memory: 2x1GB PC6400 DDR2 800MHz SO-DIMM ($39.99)
  
• HDD: 1GB Western Digital Caviar Green ($84.99)
  
• OS: Mythubuntu (+ XBMC or boxee) ($0.00, but to get guide information, it’s $20.00/year)
  
• Remote (optional): Anyware GP-IR01BK ($24.99)
  
• Optical Drive (optional): LG BD-ROM ($109.99) – I can do without this initially.
  

So, that’s $413.91 + $20/year (or $548.89 with optional stuff).

The real difference without the subscription fee is the tuner and the OS, so that difference is about $60 between a Linux build and a Windows build. However, considering that Linux can run with a slightly lower spec (RAM, for example), it could actually be close to $100.

I think the guide data used to be free, but now it’s not. So, with $100, that’s 5-year’s worth of guide data… Not so sure about that…

Update: It seems Zotac announced a new ION board with a PCI-e 1x slot, IONITX-G-E “Synergy”. It’s MSRP is $139.99 and supposedly, it’s already released in Europe. This would be a good alternative.