Loftur Jónasson built an RF Power Meter.
Lofture says that it was simple to build. It uses a Teensy ++ to sample from an AD8307 logarithmic amplifier from Analog Devices, 200 times per second. A Rotary Encoder with a built in Pushbutton is used to navigate the various displays and to access a settings/configuration menu..
The project web page has a detailed write up and includes the code for the project.