The ELM Bluetooth OBDII scanner from Amazon is like $12-15 and should be a quick setup with free phone apps. I've had one for 6-7 years, and it's not bad for limited use.
After that, look into various gauges like Aeroforce, PLX, and others that get into the $150-200 realm. Not sure anything's in between. Beyond that, you might as well go for HPTuners at $300-500, for full tuning ability.
It's all based on the app. I've used Torque Pro, ChevroSys, and tried a couple others for free (some are maybe $5). Do some research on what each offers, try the free ones when you get the ELM, and check out various YouTube videos that may go into better detail with examples.
Google and YouTube can pretty much educate you on building anything, if you're paying attention and dig enough.
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