soundcard: Audigy £80 ish
speakers: creative 5300 £80 ish (waste, rarely use), technics headphones £25 (bargain)
vid card: 9800pro £200 ish
monitor: syncmaster 757DFX £180
except for the vid card these purchases were 1 to 2+ years ago.
imo though, cant really compare. something like an Audigy 2, maybe even onboard soundstorm is actually more than perfectly good quality audio for gaming and OTT for MP3 - even fine for CDs. You can get enough out of it with a decent pair of headphones, and gamers are miles better off with headphones to speakers - how many games have good 5.1 sound anyway? All I'm bothered about is that the positional audio is good*, and the quality isnt bad.
Good audio just doesnt cost as much as a good gamer videocard, and it doesnt need to. Its well worth spending extra on a quality monitor also.
* Always hilarious listening to some newbie stomping about, reloading etc and then when you ambush him he accuses you of wallhack because you knew he was there.