What are you wanting to do? They vary a lot.
You can get an OBD II reader that can read/reset some simple codes for under $15 shipped.
https://www.walmart.com/ip/MS309-OB...MIocaIw4WB4gIVS1gNCh1BYQ72EAQYCCABEgKj5vD_BwE
That doesn’t mean for that price you can get the capabilities of tools like the Snap On Solus or Modus and countless less expensive and capable units that have access to Body control, transmission, ABS, SRS controllers, security, etc but they are thousands of dollars more expensive and still can’t do everything.
There are some fairly cheap brand specific tools you can use with a lap top that can do things like turn off the TPMS on vehicles that the dealerships claim can’t even be done. FORscan for Fords and ProCal for Jeep. Lots of stuff out there just have to know what your wanting and how much your willing to spend.
There are also Bluetooth scanners that with an app can give you some data on your phone like OBDlink and BlueDriver. If you get one of these, don’t leave them plugged in when not in use or they will kill your battery.
I keep the cheap ones all over the place because they are handy (and cheap) will get you buy for most things, a trip to many autoparts stores will get you the same thing for free if your really cheap. They just don’t do everything that can be done, they are really just code read/erase devices (and not all of them).
They keep making things more complex and having everything running on a network of various control modules. It’s not always like the old days where you find a bad part and replace it and your good. In some cases you can have something like a bad transmission, replace it with a new one and if you don’t reset all the adaptive parameters, you’ll burn the new one up in a few miles.
The goal is to make things so complex people don’t do things for themselves. A number of cars these days don’t even come with a way for the owner to check transmission fluid level. Just a matter of time before you’ll need a special tool to pop the hood.