MSI A520M PRO AMD Ryzen 5 5500F Motherboard CPU Bundle

MSI A520M PRO motherboard and AMD Ryzen 5 5500 processor bundle DDR4 support PCIe connectivity Six-core processor
Seems like a good option if you have an old pc intel 6th-9th gen, simply use ddr4 and SSD from current build and replace Mobo and CPU with this.
If you want a cheap steam machine simply add a cheap 6500xt for a lowend steam machine