You have a problem with your question. There are *NO* cheap *AND* reliable places to get Windows. I bought my win 8.1 Pro Retail off ebay for 22USD, and it has proven to be an authentic key for well over a year now and verified by Microsoft. HOWEVER, if you get it cheap, there's no way of knowing how they came about that copy, if it's actually pirated (China puts out some very convincing looking pirated software), or if it's a trial or something similar to that. Buy from a reputable retailer, reliable. Buy cheap, maybe buy it three or four times or more until you get an authentic copy. There are cheap copies out there, as stated before, but I got lucky and can not recommend it with how many stories of scams I've heard.