the price difference between the console and PC has been dropping over the years though, i remember my mega drive costing £150 at launch, when the ps3 launched at £379 and with the ps4 rumoured to be launching at either £400 or £450 depending on which rumour you beleive.
You can spec out a PC with an AMD 8 core 8GB ram and a 6870 which are the components the ps4 is meant to be based around for almost exactly the same cost and itll play the same games at 1280x720@30fps (which is what almost all console games run at even the next gen ones) as the consoles themselves, since the 6870 has an hdmi port you can even use the same TV instead of a monitor if it less than 5 years old or so.
so even if you must buy a seperate device a console isnt much cheaper, if any
You can spec out a PC with an AMD 8 core 8GB ram and a 6870 which are the components the ps4 is meant to be based around for almost exactly the same cost and itll play the same games at 1280x720@30fps (which is what almost all console games run at even the next gen ones) as the consoles themselves, since the 6870 has an hdmi port you can even use the same TV instead of a monitor if it less than 5 years old or so.
so even if you must buy a seperate device a console isnt much cheaper, if any