I've sold two spare sets of 1991 in the past 6 weeks on ebay and got about $95 for each (the second I offered to the second highest bidder on the first set). Neither set was mint, both had a lot of mint/near mint cards, but a few showing wear, particularly the green Kangaroo tour cards - and I gave a fair description. I was pretty happy, having previously sold a similar standard 91 set and got closer to $50-$60.
I've only sold an okay condition 92 set and got about $35. 93 is much more interesting. I've sold an incomplete set before (maybe 10 cards short) and picked up $70, but sold a full set recently (after seeing someone's go for over $100) and only got a couple nibbles and it went for about $45.
On ebay sometimes comes down to which way the wind is blowing.