

I’ve made a couple electronics orders recently where my order seemingly just slipped into a void somewhere (no confirmation email, no tracking info) and then just showed up at my door two weeks later. I think Amazon has made us all forget what ordering things from the internet used to be like.
PC Part Picker has filters that will let you set all your requirements and show you what’s available. Since you want ECC and low cost, you might be better off finding options on PCPartPicker and then looking for those items used on ebay.
If you don’t have a case already, you might check out Fractal Design. They have several cases for lots of 3.5" drives. I have a Define 6 and it holds like 12 3.5" and 4 2.5" in a midtower format and it’s constructed really well. You will need to buy additional drive trays though as they only come with 4 I think.