You can try to find Ryzen 5 1600 which isnt much slower than the R5 2600.
For ram Dual channel 2666 or more. (8GB is kinda minimum).
Motherboard, well now the issue is if you can find x470 or x370 motherboards for normal used price, you can then upgrade to the ryzen 3 3xxx
Storage, well this is kinda tricky, you can buy used, but then you dont know, how many hours its used (unless the seller specifies with screenshot, ask him the ID number of the
HDD and the screenshot of the HDtune or hdd sentinel should provide that), m.2 are quite cheap for me.
PSU, RX 580 is kinda powerhog, soo an good PSU is recommended as the future upgrades soo it can last longer.
Well you can get the corsair Grey label sticker which are newer than those green and orange.
CX550M/650 they should come new at 50-60€.
GPU you can buy RX 480/580 for quite cheap , 100€.
You may go over budget with the x 470 motherboard, you may pick b350 or b450 instead.