I bet that /8 went for more than the "average" value of an IP address. Larger contiguous blocks are more useful, and having a /8 has got to have some prestige value as well.
I've talked to our resident backbone engineer about that about a year ago, and he said that larger blocks transfer for a lower value per IP, on average. I was surprised by that, but he showed me data that supported that.
> As we head into the last half of 2018, small blocks are selling for just over $18/number, mid-blocks are in the $15-$18/number range, and large blocks have surpassed the $20/number threshold
so it seems there's a bit of an U shape, where mid-sized blocks have the lowest price per address.
I think this makes sense. A lot of networks need a few addresses, so /24 - /22 is probably pretty active, and you have to justify the addresses, so someone who really only needs a /24 isn't able to buy a /21 and make it work; very few people need huge swaths, but those will be able to really use them and may value having them contiguous. In the middle, it doesn't make much difference having a /16 or two /17s or four /18s, so there's a lot more flexibility, and you take the lowest price per IP if there's a block you can use.
But on the other hand, wholesale items are rarely sold at piece prices. I'm not sure the price increased that much just by having a large block. Are there other big blocks sold for known prices?
Update: I just found http://www.circleid.com/posts/20180731_the_ipv4_market_2018_... which says
> As we head into the last half of 2018, small blocks are selling for just over $18/number, mid-blocks are in the $15-$18/number range, and large blocks have surpassed the $20/number threshold
so it seems there's a bit of an U shape, where mid-sized blocks have the lowest price per address.