I've updated at least 6 Windows 7 or Windows 8 computers to windows 10 for free. If you install the right version (home or pro) and hit "I don't have a license key" when installing from a USB stick, it will go out to the internet, check for your original license, and activate. Chances are you had Windows 8 home.
If you do need a good laptop for cheap, go on ebay and buy an HP Probook 650 G1 or an HP Probook 640 G1 with a Core-i5 processor, solid state hard drive and 8 gb of ram (though they are easy to upgrade since the entire bottom of the computer slides off). For under $200, its hard to get a better computer. My family and friends have 7 of them combined. It's a corporate computer so they pretty much all came with Win 7 or Win 8 pro. They also have DVD-RW drives, good wifi, speakers aren't terrible, and the batteries also usually last.
