LOL, if you only plan to make 4-6 grand a year you don't need any meters.
Guide to water damage without meters or training:
You know if the floor is wet if your socks get wet, and if you push real hard on the drywall and if your finger goes through it you will need to follow the instructions below.
Just get a dozen Sham Wows to sop up what's on the floor.
To get the moisture out of the drywall just tape one end of a string to the drywall and put the other end into a glass. The water will adsorb into the string and fall into the glass. (don't confuse adsorb with absorb)