New
#11
The least expensive licenses that are intended for installation on a new PC are System Builder (generic OEM) ones. You're supposed to sell the PC rather than keep it for personal use, but as far as I know, there is no enforcement of that.
Newegg.com - Software, Operating Systems, OEM
Home Premium, $100. Pro, $140. Ultimate, $189.
For most users, Ultimate is damned silly.