Need Help Building a budget PC for non-intensive gaming.

I haven't been keeping up pc building for a very long time now and I need some help building a budget system for my gf. She doesn't play any intensive games, just some Teamfight Tactics (TFT) + school work in engineering (matlab, excel, CAD...etc) so no need for anything too powerful. We reside in BC, Canada. The prices for ram is bonkers right now so I was thinking I go with an older am4 platform with a Ryzen 5 chip. As for the GPU, should I go with the R5 5600g or get a used graphics off FB marketplace? Is something like a GTX 1660ti/super for $100CAD or a GTX 1080/ti for around $150CAD a good deal? Also, are used power supplies safe or should I just buy a new one? As for budget, I think I can spend around $500 CAD and maybe stretch it to $600 considering ram prices. I want to try building the case myself out of wood, so let's exclude it from budget for now.

Additionally, I need some tips on buying used gpu's or any used pc components for that matter since I've never done it. Let me know if I need to provide more information. Thank you