I built my i7-920 1.5 years ago for about $1000...but that doesn't include the monitor & graphic card. Probably cheaper now, dunno. No water cooling necessary, haha. But that's building it from parts yourself, not buying pre-made. Just tossing that out there for comparison to the "maybe $500" price.
I don't know what you all consider an "expensive" PC or what constitutes "good" graphics,
It's funny because I generally don't care too much about the overall graphic "look" of a game, but stuff like pronounced jaggies drives me crazy these days. Other than that, as long as it looks sharp and clear w/good contrast I'm happy.
Like mentioned, FNV w/out mods is never going to look graphic-uber, but it can look pretty nice in certain lighting conditions w/HDR, AA/AF, high view distances and LOD land quality higher than 100 etc.
Nevada Skies is pretty cool. I also used the Imaginator mod to make NV Skies gratingly over-saturated colors more tolerable. Some of the color filters NV Skies uses does horrible things to skin tones & I don't like cartoony saturation. But the rain and sand storms make it worth it. I also made the Pip boy light brighter because those nights are way too dark for me. lol