Pine64 are pretty good for CPU and RAM, but you will be loosing out on the great support things like Raspberry Pi SBCs have
Edit: forgot to mention Pine64 starts at like 15 usd for 512Mb Ram or 19 usd for 1GB and like 29USd for 2Gb also from 19 usd up they have gigabit(can be hard to max out due to various issues IIRC, check forum), and the high end version is still cheaper than a RPi3 IIRC