Engine Swap? 3.1V6 to a ??V8?

i was thinkin of putting a new engine in my car, of course not new, something i'd rip from a junkyard, i was wondering how big i could go inside a 96 century's hood. i would love to go to a big ol' V8 but a V6 is good too. i'd prefer a V8 but i dont know how much junkyards price there engines. and i was wondering if this is a weekend project or a week project, so then i will know if i need to take a week off of work or not. maybe i could rip an engine out of a firebird or a camaro, ill keep lookin, but i was wondering if any of you have done an engine swap and if you could give me any tips, and maybe a price range of what i need to save up to :D DUDE THANX WOOWOOOOOOO, now im excited. l8r