Practically nothing? Are there tier-1 providers charging for IP space now? I can confirm that neither Level3 nor Global Crossing charge for IP allocations as of a month ago.
(The whole "charging for IP addresses" racket always left a bad taste in my mouth, since it's a public resource for which ISPs aren't paying, other than the overhead of being expected to justify and account for the space they've been allocated.)
That's just retail markup. If you peer with tier 1 transit providers you can still get IPv4 space for practically nothing.