Hi Bubba. I think you might want to browse the library, used book store, or Amazon for a children's beginning piano or theory book. These options should be thrifty. There are online resources at the Psaltery Pstudents site, but one can get overwhelmed with online options. Best wishes as you learn your new skill!
Did your psaltery come with the notes marked or a sheet of paper you can put on it that lines up with and names the notes? This is a wonderful thing when you start out and if you get sheet music that has the name of the note printed on the note you can match them up and it will help you learn the music more quickly. The Westmans music is called "noted note" and the Psaltery Strings book also has the note names.
Check out the Westmans at WestmanInstruments.com and the Psaltery Strings book can be purchased here
If you don't have markers for your notes maybe we can help you out with that!
I am learning to read music also. I found a good source of information on youtube. It is called music education for all. Their segments on learning to count music was very helpful