Build a mini-ITX rig and it’ll cost you $700-$900 depending on the graphic card.
Go for AMD A10 or similar chips, they are faster for the price it comes in and pretty good for gaming. You could wait for Jaguar line of processors before you start. These rigs not only use less power but are also quieter generally.
The advantage of going for a smaller PC is that you can hook it up to your livingroom TV and even use Steam Big Picture mode to game, which is a lot of fun. Additionally you can also get a TV tuner card and use it as a media centre PC when you feel like it. That way you don’t need to wait for Xbox One or buy another device for streaming your media.
HTC One is a great device as the hardware goes, but it looks very different from other Android device and that puts people off. I’m waiting for the day Google starts selling an HTC Nexus One to buy it.