Win 8 moves ~40,000,000 licenses in first month. Upgrades are $39.99. Win 7 moved ~30,000,000 in month one. Upgrades were $120 - 220/upgrade. Vista moved 20,000,000 first month. Upgrades were $129 - 299. MSFT is offering the DVD-version of Windows 8 for ~$30/more per copy so let's just pretend that the fair price for comparison of Windows 8 is $69.99 (since I assume far more physical media went out of Win 7 in 2009).…
[1] see http://www.tomshardware.com/news/windows-7-upgrade-discount-..., for instance