If you can spare the money, you can buy a pretty decent prebuilt gaming pc on Ebay for around $600 usd. I paid $500 for mine and it runs most games pretty well. Or you can slowly upgrade yours piece by piece when you can afford it, and there might still be free Windows 10 updates.
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You really cant find cheaper pc's then around that maximum price.
Look here: https://www.ebay.com/sch/i.html?_from=R40&_nkw=pc&_sacat=0&RAM%2520Size=8%2520GB...
(Ebay) and you might find something cheaper. There you have some computers but it's up to you.
At least they exist so you can get a computer that is what you call today as a decent computer...