Innovate Motorsports makes a mix of gauges and controllers that get the job done without braking the bank. You can either go with a digital or analog gauge that reads A/F or a controller that will connect to a gauge. They have serial in and out connections and can be linked together with other IMS devices including data recorder that puts a run on an SD card.
I have a chain consisting of an LC-2 to read A/F, a G-3 gauge to display it, an SSI-4 PLUS interface to add RPM and three other channels down the road and an a PL-1 Pocket Logger to record data.
Stay away from the LM2. It's very picky about voltage.
https://www.innovatemotorsports.com/
EDIT: If you want to play with one, I have an out of production digital gauge from them that is yours for shipping. PM me if you want it.