[rkcarguy]

I have a wideband O2 sensor and display that I bought for tuning purposes, it displays 10:1 up to 20:1 AFR's.
You have to have an extra O2 bung welded into your exhaust, the display can just plug into the cigarette lighter.
Expect to spend ~$200 though unless you get lucky and find a used one.
You can also tap into the right wires at the ecu and get a voltage readout at the stock sensor that you should be able to convert to approx AFR if you do some research.
There 02 sensor should have a heater wire, ground, + constant, and + variable(O2 reading).