

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.
I think the Define 5 is a good option as well. I bought the 6 in 2018 because it was new, was white, and only like $99 at the time and it’s served me well. Every couple of years I’d buy some more drive trays as my pool filled up and I needed more space.
I just rebuilt my whole system a couple of months ago but kept the case because it works so well and there isn’t much on the market like it without getting into fullsize cases. It’s nearly silent even with 5 fans and 9 HDDs inside. It sits about 2 feet from me on my desk and I only hear a tiny hum from the fans.