How much does a Windows 7 startup disc cost?

I assume you need a license also. Windows 7 Home Premium sells for $200, or $120 if you're upgrading from a (properly licensed and legitimate) previous version of Windows.

If you bought a new computer with Windows preinstalled and it didn't come with an install disk, contact the manufacturer. They usually sell the discs for a nuisance fee ($5-$20 or so), because you're SUPPOSED to create your own recovery discs as soon as you get the computer (though I'm not sure how many people actually bother).