The way I see it you have two options:
1) Have the fun of building yourself and get a high-end result, but this is not cheaper anymore like it was back in the day... usually costs more now, but you can get exactly what you want.
2) Buy pre-made and $ave. I find nowadays that pre-made systems are often of more than sufficient quality and performance.
If I were in the HTPC market I'd be tempted to buy pre-made from someone like:
http://www.moneual.com/I have no experience with their products, but one of their ads in a magazine caught my eye. Looks like pretty slick gear.
Hmm, after a look at their shop, the prices are not so cheap - kinda high-end. The price of your selected parts is comparable to similar discussions:
http://www.zdnet.com/blog/hardware/build-your-own-home-theater-pc-htpc-for-under-600/7123Maybe it is still cheaper to build your own.
In the area of HTPC applications I'd stay away from a laptop as a solution, for lifetime reasons (lack of cooling, built to self-destruct, planned obsolescence, etc...).
An interesting article on the subject:
http://www.engadget.com/2011/01/14/the-home-theater-pc-is-dead-long-live-windows-media-center/that is where I landed.
ASRock and Zotac seem to be the names in this no-mans-land market. (I'm tempted to start looking at building and selling these rigs myself.) In a dream, I am the proprietor of my own futuretech audiophile shop...
The Zotac ZBOX-AD03BR-U appears to sell for under $500 and the ASRock Vision 3D 137B appears to sell for under $1000.