Need Advice on Minecraft computer for my son budget $500

If you're just running Minecraft, you don't need anything fancy at all. At $500, honestly I would just recommend purchasing the Powerspec B245. Minecraft is very light for system requirements. A light GPU with 8GB of RAM and 4-core processor are all you would need to run it very well. 

When you include the cost of Windows, it's usually better to purchase a pre-built system on a tight budget like this. Windows is an extra $120-140 and that makes it difficult to fit in other parts at this price point. If you really want to build one yourself, you could put together something like this:

https://www.microcenter.com/site/content/custom-pc-builder.aspx?load=8785e594-13d6-42f3-9fb6-0fea087ae4d5

The Ryzen 3 3200G is a pretty good little budget processor, and the integrated Vega 8 graphics on it are actually pretty decent, far better than the integrated graphics on Intel's CPUs. It can definitely run Minecraft, and we manage to fit in an SSD with a decent amount of storage space. The main difference with this build vs the Powerspec is that the Powerspec comes with a Ryzen 5 3400G which is a better processor with slightly better integrated graphics, which is why I'd recommend it over going the custom-build route. It's just a little better value for the same price, and will be better if you ever plan to upgrade the system in the future by adding a video card.