If you prefer to buy a prebuilt pc (obviously everyone here is going to recommend that you build it yourself) then cyberpowerpc and ibuypower are both general run of the mill pc building sites. You will spend a little extra to buy a pc from them (they have to make money somehow) And generally they do this buy charging you extra for the parts.
I've found for me that the best way to circumvent this and save yourself the hassle is buying a prebuilt that has a great processor / mobo set up, and get the cheapest GPU, SSD, and RAM possible. Then when you get the PC you upgrade those things yourself, that way you have the PC you want, and you have those original parts as back ups in case something fails.
This isn't a perfect solution because you will end up spending more than you really should, but I think it's a good compromise.
If you do use one of these websites, I suggest that you select the components manually, if you leave the fields blank to indicate things like "16GB of DDR4 RAM" but don't manually select a brand, these companies will put non-namebrand parts that you likely have never heard of in the pc. If you are fine with that, then go with that option, but I'd rather have parts from a manufacturer that I know builds quality parts (not to say that those name brands couldn't be cheap and poor quality either though)