Ed,
The best way to gauge that is to visit eBay or Reverb.com and do a search of sold listings and determine an average sold price. You may need to read a lot about each guitar's condition, or view the sold listing images. An average of 5 or 6 sold listings of your model guitar will provide you with an appropriate number. Also, if the guitar you're trying to estimate worth of is a more rare guitar, an average of 2 or 3 is adequate.
And TBH, Is the semi-hollow chambered, or does the guitar have a violin-like f-holes? When you post a few more posts, you'll be able to post images of the guitar so we'll have a clearer idea of what you're writing about.