Well, for the age I was, my SNES. I payed heck like $150-$200 for it. I don't even remember it was sooooo long ago. I saved for more than a year and bought it at launch....
(Brief pause to check Wikipedia)
Ok the SNES was released in 1991. I was born in '82, so at the time I was 9. Freaking NINE years old when I saved up $199 and bought that bad boy. My family wasn't rich either so when I say I saved for a year, I'm serious. I got Zelda for Christmas that year. It was soooooo blissful. I just remember being so happy and shocked. Good times.
Most expensive game? I don't remember paying too much for any of them, but I suppose it was probably FFIV or FFVI (FF2 and FF3 US). Either that or Oblivion a couple weeks ago!
Jam it back in, in the dark.