I would suggest to build a PC that too in $500 budget approx. There are 2-3 guides I read when I want to build the same.
What is the point of doing that? That is literally a waste of money and you are better off spending the entire $3k on the laptop itself because that will give you much better performance than a $500 PC.
If you allocate $500 to laptop and rest to PC you are making better use of your money. Heck, taking the laptop budget to $800 or even $1000 and using the rest for the PC will still give you VERY good builds.