There is a guy on Hardforum selling a 48TB NAS made only of m.2 SATA drives. Was asking 3800 USD I think. From his post :
48TB SSD storage subsystem. Looking to sell this as a group, but if I can account for all of the SSDs and the 24-port HBA, I’ll part it out. If you want the entire thing as it is setup, I will include a 150W picoPSU with the custom-made SATA power cables (will power this no problem as long as you have a reasonable CPU tdp – I used a supermicro X10sdv-TL4NF+ for my FreeNAS box). This will fit in a 2U case, height-wise, and generally takes up the same amount of space as two 3.5" HDDs.
$3800 + shipping
- 24x 2TB Western Digital Blue m.2 SATA SSDs (WDS200T2B0B drives)
- LSI 9305-24i HBA
- 8x modified (shortened PCB and additional mounting holes drilled) quad-m.2 adapters (you get two extra that I had laying around

)
- 6x HBA cables for this setup
- 150W pico-PSU with 2x triple SATA power connectors
here is the backplane that was used. Crafty!