Looking for good Minecraft Desktop PC I could buy with $450 - $600. I hope I could get about 75 + FPS and can record and download mods. Any?

Ye

You could run Minecraft on a f-ing flip phone and get 75+ fps if you installed optifine. But Minecraft is almost entirely CPU-bound unless you're using very intensive shaders, in which case you can easily go over $600 with a good GPU. But if your display isn't above 60hz, you could bet 3000 fps and all you'd see is 60 with horrible screen tearing.

If you want also a monitor, mouse, keyboard, and a Windows some version license with that "Desktop PC", then none that I have seen anywhere. You will have to spend more.