Sunwayfoto has an Arca-copmatible L-plate (similar to the Really Right Stuff plate)¹. Apparently it introduced at $60, but as of 2016-03-02, I was able to find it for < $20 USD on Amazon.
Notably, the Sunwayfoto plate appears to allow more downward angle of the LCD than the RRS plate does.
Articles describing the Sunwayfoto plate:
- original PSL-a7 plate
- improved PSL-a7II plate (not for Sony a7 Mark II camera. Confusing product naming, I know).
¹ Note: often times, "Arca-compatible" is a loose definition. If you use a lever-action Arca-type clamp, this plate might not be compatible (according to some of the Amazon reviews). However, if your Arca-type clamp uses a screw knob to tighten the jaws, this plate (or any Arca-type plate) will work fine.