Here are a couple of YouTube videos from Newegg about building your own PC.
This is a good way to get a PC that has a reset header on the motherboard for a PC Watchdog as well as getting a front panel reset button.
Once you have built the PC you will have access to spare parts quickly from Newegg or other online sources. You will also have access to local sources for spare parts as well such as Fry's, Best Buy, or Walmart.
This is just one sample of the many videos on YouTube. Search for more with: "build your own PC"