If you don't have any technical experience I imagine building your own even with used parts would be a bit daunting. However If you are willing to learn and do the work I'd recommend getting one of these: https://www.parkytowers.me.uk/thin/hp/t620/

You can pair that with a basic 1TB m.2 SATA SSD (check prices here: https://diskprices.com)

Then install start9, umbrel, etc should be pretty easy.