I was shocked to find this out but my current provider has pushed the price up to £10 for 1 IPv4 address. I purchased one a few years ago for £2.50. I was so shocked by the price increase, I asked my provider and they told me it was down to demand. So I can see this being a wide spread issue.
From what I can see, there is around 40% of my website visitors are using IPv6, things are looking pretty good actually. IPv4's prices are starting to go down. 3-4 months ago an IP block can sell at $50+ per IP, this is now in the $40-50 range.