The cheaper ones you see online are most likely the OEM version (usually around $90), which once installed, is tied to the motherboard of that system and cannot be transferred. If you want a physical copy buying from a store like Best Buy is probably the best you can do. To avoid sales tax one option is to buy from Newegg if you live somewhere they don't charge, but like you said that involves waiting for shipping. I prefer to buy a digital copy and create an installation usb stick since it's the exact same thing you get on the physical media you bought, but that obviously also means another system has to be available to create the installation media in the first place.
So buying retail means I can transfer the OS as much as I like, but OEM locks it to a single motherboard?
Yes, the Full Retail version (which should be the one you got, based on the price) is able to be transferred between systems, useful if you swap your motherboard or build a new system in the future. I believe it first has to be deactivated on the old device before being able to activate on the new one, but you could verify with MS support on that.
Thanks :) ok, so I have everything ready to install Win10, but the USB that comes in the little box that has Win10 on it, is only pro and doesn't give me the option for home edition even though that's exactly what I bought :\ Also, the media creation tool seems to give me standard edition. Just shows "Windows 10" in the Edition box.
So now I'm not sure what to do without losing any files :\ I can't backup everything, but I did copy some things to my HDD.
So you bought Home edition and got Pro? If it really is Pro, they just sold you the wrong edition, won't make a difference for you though. There's no "Standard" edition, it's Home or Pro, and 32 or 64 bit (you want to install 64 bit).
I'm not sure I understand, you're installing Windows on a drive that already has an OS on it, or that just has some files on it? Every time I've fresh installed Windows it's been on a formatted drive, so I don't have any experience with that. Some Google searches seem to indicate it is ok, but you might want to post a new thread explaining exactly what you're trying to do, let someone who knows for sure give you a good answer.