Best Affordable Diagnostic Scanner for people, who are tired of getting ripped off.

I'm a senior lady with no formal auto mechanical experience.  And I don't have anyone I can trust to help me diagnose problems with my 2000 Toyota Echo.  Recently, I took my Echo to a local CarX shop, who told me I needed a new AC compressor.  They wanted $1,600.  But I decided to just have the belts replaced at that time.  The squeal that I heard intermittently when I turned on the heater, and that I had started to hear when I turn on the ignition, was no longer there.  I wondered if I should still have the AC compressor replaced until I luckily found a shop ( 160-miles away from where I live with lots of 5-star customer reviews and legitimate community ties) tell me that I probably did not need a new AC compressor.  He offered to look at my Echo, but after he explained why he thought I did not need a new AC compressor and that he thought I was being taken advantage of, I decided to just see how things go.  I made a 100-mile trip recently and I had no problems ( knock on wood).  My Echo seems to "ride" even better now actually.  Anyway, since I can't seem to find a mechanic I can trust close to my home, I want to try and diagnose my car if and when problems come up.  Could someone please give me the names of some affordable ( $150 or less) OBD diagnostic scanners out there for people without any formal auto mechanic experience?  I can look up the codes online, so that at least I might have a fighting chance if I need to have work done that I can't do myself.  I am also looking for another older used car, so a good scanner would come in very handy for that also.