https://www.amazon.com/AMD-Ryzen-3200G-Unlocked-Processor/dp/B07STGHZK8/ref=mp_s_a_1_4?dchild=1&keywords=ryzen+3+3100&qid=1606223860&sr=8-4 and https://www.amazon.com/Intel-i3-9100F-Desktop-Processor-Graphics/dp/B07R7Q3JZH/ref=mp_s_a_1_1?dchild=1&keywords=intel+3+9100f&qid=1606223952&sr=8-1 if you go intel, https://www.amazon.com/GIGABYTE-H310M-2-0-LGA1151-Motherboard/dp/B07Q6264RX/ref=mp_s_a_1_1?dchild=1&keywords=gigabyte+b450m+ds3h+intel&qid=1606224007&sr=8-1 this a intel version of the other mb, and its easy to find 16gb ram for like 50$ but you can go 8gb, then upgrade later.

https://www.amazon.com/GIGABYTE-H310M-2-0-LGA1151-Motherboard/dp/B07Q6264RX This motherboard should work for you