The Oak Hills research produce a very nice QRP power meter kit, the RF power meter WM-2 QRP is produced with a high quality case and silkscreened and masked PCB and a large moving coil meter.
Operates from 300 KHz to 54 MHz
Measured power range from 100 mW to 10W FSD with an accuracy of 5%
I built one a few years ago, and found it very helpful when measuring QRP power from the FT817 and Ultimate 3 QRP kits.
The kit comes with everything you need, instructions are provided in the pack and takes a few hrs to build. The kits are available online and currently cost $129.95 and can be provided with BNC or SO239 sockets.
You can calibrate the meter without the need for any special test equipment.
Ive included some pictures of the completed meter, and think you will agree it looks very professional. Power is provided by a 9v battery or external supply.