

Just get a bigger combination air fryer/toaster oven. They’re a total game changer and way more efficient than using your kitchen oven. I haven’t found a frozen pizza yet that won’t fit inside ours, there’s almost zero preheating time, and the air fryer portion works great for fries, tots, nuggets, etc.
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.