A:
You wouldnt need a restore disk if your uninstalling windows and wanted to reinstall it later. You would need an install disk. here's a. Example as far as pricing for Windows 7 Home Premium as an example. Oviously it would be more if you were to get something better like the Professional or Ultimate version though
http://www.bestbuy.com/site/windows-7-home-premium-with-service-pack-1-64-bit-license-and-media-1-pc-windows/5130359.p?id=1219111161659&skuId=5130359