refurbished engine vs second hand engine

[Dezaman]

imma sound like a complete dumbshit asking this but this is the only car related forum im attached to, so i owned an ex taxi, its gone now but it was on its second engine, the second engine was a refurbished engine, i know the theory behind a refurbished engine, its a second hand engine thats had the major parts that need replacing replaced so its like new, simple enough, but expensive, im thinking of purchasing another au (i couldnt resist im way to poor for a ba yet au's are so comfy even if they like spinning out) with redicously high km's, the original idea was to do what i always do and drive it till it dies a terrible death and buy a new engine, but how could i go to refurbish the engine by myself, what parts need replacing, new heads, new headgaskets, spark plugs, itd be a whole lot cheaper to do it myself then buy a new engine rite? the engines at 350,000 what can i do to get it running another 100,000 and will it cost me more then 400-500 bucks (the price i think reasonable for a new engine) thanks guys Deza