Greetings @yolo Good build overall. Assuming you're trying to save without sacrificing performance the only fat to trim is the motherboard. If you're not overclocking and don't need any specific features of this board, you could save $40-50 on a lower end board.
What kind of prebuilt PC do you have, do you know what PSU is in it? Depending on what PSU you have you may be able to keep that around as well.
That doesn't offer any information about the PSU unfortunately, but with an RX580 it's probably a 450W or 500W PSU which is usually good for budget and mid-range cards. We don't know what the power draw looks like for the upcoming RTX cards yet, but NVIDIA is recommending a 650W PSU for the 3070. In reality manufacturers usually over-shoot recommendations to be safe and you may be able to run the 3070 with a 500W PSU but we don't know for sure until we get more information from reviews.
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