We have been brokering IPv4 addresses for many years, we brokered half the bids for the watershed sale of 660,000 addresses from Nortel to Microsoft in 2011. Because of the inter-regional transfers allowed between ARIN and APNIC, we consider that a single market. ARIN/APNIC prices are right around $8US per address. RIPE has no inter-regional transfer policy, and prices in RIPE are around $10US per address. Leasing of space is also available.