If you're buying Raspberry Pi's, either the form factor or power requirements really worked for you, such as if you're in robotics, IoT sensors, or hardware-adjacent stuff, or you knew you were spending a little bit extra for the hobby space.
That includes all the people setting up home labs for their own learning. An M1 is about $250 refurbished under Amazon's protection program. If you intend to use this as a hybrid device, which many frugal people do, then you'll also likely be using this as a desktop device connected to a monitor. The cost of electricity will rival your purchase in a year.
If you're gonna buy a throwaway computer for a child to experiment with, IMO a used Mac Mini delivers unbelievable price efficiency as a general-purpose computer. Use it as a server, use it for programming, use it for homework.
If you are going down this path, an N150 machine is cheaper, more flexible (Windows), more readily available, brand new, and performant enough for all the above use-cases. An old Mac Mini makes no sense to me.
Ah, the N150 machines are around $400-500 for me in the NUC. In that case it'd make sense to go for a new M4 Mini for $400 at Costco or student prices.
They are £150-£250 on Amazon right now. Cheaper if you buy elsewhere and wait 2 weeks for delivery. $400 is not a realistic price, are you looking at something else?
I asked for a new one, and I am not going to pay such prices for 2nd hand stuff, assuming they exist at all, cheapest is 320 € on Amazon Germany.