I found mine at Lowes, I think it was like $11 its a light/moisture/ph combo meter, but try to get in a habit of feeling the weight dry/wet. I hardly ever use that thing, its cheap but its o.k. to start out with
Stick your finger 2" into your soil(make sure your hands are clean) usually up to your knuckle, if its dry, water them...but remember you need to let the soil dry out a bit so the roots go searching for that water, so you promote good root growth
i got a decent one at a local nursery/garden supply store for $20. The big problem I was having was that my soil had a different moisture reading at different places around the pot.
I also used my finger a lot, and lifted the pots to see how heavy they were.