Seen this power meter yet?
http://www.powerpodsports.com/
Review by DC Rainmaker is very positive. Accuracy and correlation with 4 other power meters on Ray's bike (and with another bike sporting 3 other meters and a third bike with another single reference meter onboard) looked pretty good for the money.
http://www.dcrainmaker.com/2016/03/powerpod-depth-review.html
$300 retail and with the 10% off code from Ray's website when purchased through Clever Training, it's downright cheap at $270.
The alternatives of a Stages single side crank arm starting around $530 or Garmin's single side Vector S2 pedals at around $700. The 4iiii unit is around $400 that's a decent unit. There is also the $100 PowerCal, but I'm not thrilled with it based on the user review information.
So $270 Wattage based on air pressure, accelerometers, RPM, cadence data? Now there's a totally new idea!