As an alternative to the Raspberry Pi 3 for a low-cost 64-bit ARM (AArch64) development board is the PINE 64, which was successfully Kickstarted as a "$15 64-bit single board super computer" that generated more than 1.7 million dollars. The PINE 64 is still shipping out in limited quantities for now, but the folks behind this project were kind enough to send over a sample of their PINE 64 1GB SBC for some benchmarking.
The PINE 64 is powered by a 64-bit quad-core ARM Cortex-A53 processor running at 1.2GHz and the SoC has a Mali 400-MP2 graphics processor. The different PINE 64 models include the base $15 unit with 512MB of RAM, the PINE 64+ with 1GB RAM (what's being tested today) for $19 USD, and the PINE 64+ 2GB with 2GB of DDR3 for $29 USD. The PINE 64+ models also support a five megapixel camera port, 4 lanes MIPI video port, and a touch panel port. Another advantage of the PINE 64+ models over the $15 PINE 64 is Gigabit Ethernet rather than 10/100. All three models besides sharing the same SoC also have two USB 2.0 ports, 4K x 2K HDMI, 3.5mm stereo output, RTC capability built-in, built-in 3.7V battery charging circuit, and a microSD slot that supports up to 256GB of storage. The pricing on these PINE 64 units does not include shipping and handling. Currently all of the models are out of stock while the PINE 64+ models are expected to next begin shipping in May.
The PINE 64+ models are spec'ed rather well for the price and hold greater possibilities thanks to the Gigabit Ethernet and 1GB+ of RAM. While a lot of people are interested in the PINE 64, unfortunately, the open-source situation with the board will be less than ideal due to the Mali-400 MP2 graphics. While there is the Lima driver project aimed at reverse-engineering ARM Mali graphics, that initiative is basically dead where at least the Raspberry Pi VC4 driver stack for Broadcom graphics is finally becoming useful in an open-source world with a proper DRM/KMS driver and Gallium3D driver.
Beyond the graphics situation, it's the Allwinner A64 SoC used by the PINE 64 and many Phoronix readers know all about Allwinner and have their own opinions about the company and Linux friendliness...
Currently, the PINE 64 project provides Linux images of Arch Linux, Remix OS, and Android.
For the benchmarking today, I was using their Arch Linux image with the Xfce 4 desktop built atop the Longsleep image spin and marked version 20160304. Imaging this Arch Linux install to a micro-SD card and booting up the PINE 64 worked immediately and I was on to testing.