Not that old. Pretty sure mine is an intel i5.

It won’t be on Amazon, but I found a ton of older generation Mac minis available on Craigslist in my area. I picked one up for $50 and installed Ubuntu server. Thing’s been running like a champ for 2 years.

Edit: should have fully read your post. No idea about installing truenas on it. I’d assume most would be single ssd machines.