I built this dedicated HTPC after using my main desktop as a headless HTPC to test out a WMC setup in the house for a few months. Everything was stable and I've been a couple months without a TWC cable box or DVR.
I decided to go to a dedicated HTPC to connect to a TV so that I could have 1 more WMC setup (vs. buying another extender) and to decouple the HTPC from the desktop. I prefer Intel based builds. Price was a minor goal but certainly not a requirement to build the least expensive system.
The setup includes the HTPC with 2 WMC Extenders (1 xbox360, 1 ceton Echo).
The HTPC build is using a spare 2.5" HDD for the OS drive that I had laying around. I considered an SSD but the performance was OK for not spending any more money. If a deal pops up on an SSD, I'll switch over.
Recordings are stored on the 2 2TB red drives (raid 1 - mirroring). The OS drive image is backed up to storage drive weekly.
OS is windows 7 which I also already had.
The setup is using a HDHomerun Prime as a tuner. Everything is connected with hardwired gigabit Ethernet.
It currently doesn't include an optical drive; I may put a DVD drive in but I already have a standalone unit.
Total price for the build was $490 from eBay (i3), newegg (ASrock, WD HDDs, Silverstone case, PSU), and Amazon (Corsair).