The M1 uses 26 under load and 39watt peak load (16GB with the 2TB ssd version according to apple). Measured with kill-a-watt, I've read 4watt idle and 20watt full load. So I think the 26watt is probably a more realistic value.
16GB version: $899 1TB usb-c ssd: $109 1U rackmount: $199
This will give you 16GB ram and 1.2TB ssd for $1207. It can fit two mac minis. As the purpose was 1U with max 1A/120V, you'd be able to run 3 mac minis in 1U (or 4 if you make sure they don't exceed 30watt).
In terms of performance the pi does 295single and 830multi. 5 rpis is 295single (does not increase with 5 rpis!) and 4150multi. The M1 does 1748single and 7660multi. So you get about twice the cpu performance (ignoring the super fast 256gb ssd, and other hardware features the M1 has, and the overhead of running a 5 node cluster).
A rackshelf for 4 mac-minis is $359. If you'd actually put in 3 (because of the 1A limit), you'd have 6x the cpu performance for somewhere between $3000 and $3300 (depending on the storage you want). All still in 1U.
If power usage can be higher, you could actually fit up to 8 mac minis (36" depth) for 2.6A @120V. The comparison table in the article compares this setup with a Dell using 2.08A ("not at peak?"). But if you consider a max of about 20watt per M1, you can host 4-6 M1s with 1A.
Also, you won't have to deal with breaking sd cards, the heat, noise, the wiring mess, and it has many hardware features that an rpi doesn't have. You won't have to deal with the storage, memory and cpu overhead of running something distributed.
Still it's fun to tinker around with rpis. Although I stopped using them, as storage is really flakey because of the SSDs. Other SBCs offer built-on ssd storage.