yeah as said it varies.
depends which auction you goto, which day you go, who is there etc.
if you get a good day with no dealers then you can pick up good bargains.
last auction i went to was an MGS one, a fair few cars there. it wasnt a big auction, mainly for industrial type things, but the cars that were there went off super cheap.
examples:
2002ish model Ford Territory, under 20thousand K's, immac condition, fully optioned model, went for $12k.
Audi A4, not sure what year, but was fairly recent, went for $6k
having said that, you could go on a day full of traders and pay a price that is totally stupid.
do a bit of research, find out a bit about who goes to what auction, and youll pick up a bargain no worries.