Well, I think alot of it is going to depend on just what you want out of it.... what kinds of games you're after on it, particularly. If you're after alot of high-end graphics type games, that's where the whole thing can get a bit annoying, in terms of selecting parts and all of that gibberish.
I used this site to put mine together: ibuypower.com
Damn stupid name for a site, but they've got this nice interface thing on there (I forget just where) that goes away from all of those pre-made models, and essentially makes it easy for you to select your own parts, every single one. It then gets custom built and sent to you. And I'm sure there's a variety of other services out there like this one. I found that it helped.... I'm very good with software, but utterly useless when it comes to handling hardware, so there's no way I could have actually assembled mine on my own. It would have exploded or something.
As pricing goes, hmm.... that bit always seems hard to get a good grasp on. Typically I see prices for PCs that are anywhere from $500 to $1200, or more, depending on what the things are built out of. Needless to say the ones on the lower range wont be nearly as good for gaming and such. Just depends on how much you're willing to spend.
Now as for the bit with the TV, yeah, that can be done. Mine has a video card (NVidia) that happens to have an HDMI output slot in it in addition to the usual stuffs. I just stuck the cable into it, and the display and such is currently duplicated onto that second screen. It was easy.
.....though that's not actually WHY I did it, I did it because the bloody audio connection decided "HERP DERP DUHHHH" and isnt working right, so the TV (sits next to monitor, and is not the right resolution to just use AS the monitor) is now being used as the world's most idiotic speakers for the PC. Whole setup is all sorts of stupid. But it did duplicate the display (with the TV being a fuzzy mess since I've not set it up for that)! Even though that's not what I needed it for.