[Build Help] Building a PC as a gift for my friend's birthday, need help finding cheap reliable parts!

I'm building my friend a PC for his birthday, But being a high school student working minimum wage doesn't really help that... I was wondering if anyone could help me find parts for a budget gaming PC that could run games like CS:GO on pretty high graphics with good frames. I would also like it to be upgrade-able obviously so that as he earns money himself, he will be able to make it better and better. My budget is as low as i can make it, I'm hoping that some people i know can pitch in some parts so i'm mainly looking for a cheap option of every internal part needing so I can purchase any piece I couldn't find from friends cheaply

Thanks for the help Reddit!