How viable/expensive would it be to pick up a copy of Windows 7 and install that on a laptop bought with Windows 8? Are Windows 8 laptops cheaper because the requirements are lower (i.e. might not run Win 7) or just because they're the current mass market laptops?
Probably very viable. Win8 is just the current edition, and uses similar architecture to 7 from what I've gathered- anything that runs 8 should run 7 and visa-versa. I have no idea about price, and most laptops come with auto-install now, so the first time you turn it on, Windows installs from the Hard Drive as opposed to from a disc that you insert, so that part of the process could be an effort.