I have a Vista machine on the bench. Looking on Google there are multiple vendors selling Win 10 licensenses for under $50. The "Official" MS site has Win 10 Home for $119.
Are these 'other' sites legit? They say you get a key for the money paid. I do have an iso download of Win 10 so is this a good deal or should I stay away from these non MS versions?

Regards,

Those sellers are probably selling volume licenses illegally or maybe just skirting the Microsoft license terms. I would stay away, especially if you are doing this as a business.