You can put together a great gaming PC for less than $500 and you wouldn't have to upgrade it until the next console generation. You also get free online play, cheaper games, exclusive content and mod support as well as a far greater body of exclusive games than the 360 or any other console could ever offer. The PC is the option that is no more expensive and yet it offers so much more.
A lot depends on what he has in his current PC (and what monitor he's using). It could be a $1000 expense or merely a $200-300 upgrade if his mobo, HDD, etc. are still current.
What PC games are slated for the next 12 months? I haven't been paying attention.
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