I've built a MythTV home media PC, attempting to keep the costs down. It's already cost $539, which is more than a Tivo HD ($299), and very close to a Tivo Series 3 ($575). The advantages over buying a TVIO include:

1. DVD / CD playback and archiving to HD.
2. Cheaper subscription costs (Free over the air, or 20-40$ a year from Schedules Direct).
3. Automatic commercial detection.
4. Open Platform, which allows for easy network mounting of file-systems, administration, and customization.

Buying the most inexpensive components I could find (sometimes used), my costs so far are:

Computer: GQ 5140 from Frys $150 (after $100 rebate)

• Celeron D 3.2Mhz (Able to play HD MPEG2 streams)
• 512 MB Ram (512 was sufficient, but I added an additional 512MB after six months for $10 to minimize the swap file usage)
• DVD/CD-RW Drive + flash media slots
• 80 GB Hard Drive (prime upgrade candidate)
• Speakers, Keyboard, Mouse

PCI Express GeForce 7200GS video card: $34
I initially went with an ATI card, but the computer didn't have enough CPU power to play full HD TV (the wife's football games) without hardware mpeg2 acceleration, so I had to go and get an nVidia card.

Quiet CPU cooler, thermal grease & case fan: $56 
The first computer I bought from Fry's died after a 24 hour cpu burn-in test, due I'm sure to the substandard CPU cooler that shipped with it. Aside from being noisy, it also wasn't very efficient, and the CPU temp would hover around 78 degrees C at full load. My second CPU lasted through the 24 hour burn-in test, and after I put a better CPU cooler on it, my top temp dropped to 70 degrees C under full load. The new fan is designed to be quiet, and the added cooling efficiency also resulted in a 15 degree C drop when idle, allowing me to use fan-control to reduce the CPU fan speed to a completely inaudible level when idle. When under full load, the fan is barely audible from 5 feet away, which is much better than the stock fan. The case fan is turned off unless the CPU is running at near it's max temp (above 55 C).

SiliconDust HDTV Networked Dual Tuner & IR Remote Receiver: $170
I was originally going to buy dual PCI pcHDTV tuner cards (which support Linux exclusively, and do not honor the broadcast flag), but when I found the SiliconDust HDTV box it had so many advantages that I changed my plans. In addition to supporting Linux, it also works with Mac's and Windows MCE (a key advantage if I ever want to sell it) plus it integrates a LIRC infrared remote control receiver, and dual tuners for $80 less than I'd have to pay for two pcHDTV cards. The fact that it streams MPEG2 streams over Ethernet (potentially to multiple computers) and doesn't take up two PCI slots makes up for the fact that I have to maintain an extra piece of hardware, plug it into the UPS, etc

RadioShack Amplified HD Antenna(#15-2186): $53
We live within 5 miles of the HD antennas, and I was hoping to get away with simple rabbit ears, but they would only pull in about half of the stations. I am very happy with this little indoor/outdoor amplified patch antenna (even if it is yet another power adapter to plug into the UPS), as it boosted signal reception to the level where we can pick up all the HD stations in the area. (The powered amplifier is key, without it, the patch antenna has worse reception than rabbit ears.) I found that putting it in a window-sil gave the best (indoor) reception, even if it was pointed in entirely the wrong direction.

20" CRT Monitor (used): $25
Purchased from a student who was moving out of his dorm, the 20" CRT monitor replaced our existing 20" television. The size isn't any bigger, but the resolution is a lot higher, plus it will go into DPMS power saving mode automatically when the MythTV interface blanks out. If we sell the TV to college students moving into the dorms, we may even come out ahead on this cost.  I had originally wanted to use the S-Video out to drive the TV, but it turned out that the Linux ATI driver had bugs supporting VideoOverlay correctly on the S-Video output. It turns out that their may be a way to fix this with the correct xorg.conf settings, but I prefer the 1600×1200 resolution of the CRT.

250 GB External USB Hard Drive (used): $60 
I eventually plan on installing a 500 to 750 GB internal SATA hard drive and using it to hold all of our media (CD's / DVD's), but that will be more expensive, plus require external backup. I mounted the 250 GB external drive under /usr/share/mythtv/recordings, which gives plenty of space for storing TV, and doesn't require me to buy another drive to back it up. Again, another item to plug into the UPS. I do have a free PATA connector and Molex in the case, so I may move the 250GB drive inside at the same time I install the to be purchased 500/750GB drive.

Extra Costs:
The following costs were prompted by me building the MYTH-TV media computer, but are not strictly required. You could buy a TIVO3 and NOT plug it into a UPS, you'd just be living dangerously.

UPS for power protection $55