If Android will do - Cortex-A53 smartphones like the Huawei Ascend Y550 cost 120€ nowdays in Europe (about 4x the price of a Raspberry Pi).
- Far too little memory (2GB vs 16/32GB+)
- Slow flash vs SATA disks
- The "zoo" of u-boot/proprietary kernel crap, instead of UEFI, ACPI and standard upstream kernels
- Nonsense like locked bootloaders (Nexus 9 disables HYP mode in the bootloader!!!)
If Android will do - Cortex-A53 smartphones like the Huawei Ascend Y550 cost 120€ nowdays in Europe (about 4x the price of a Raspberry Pi).