What is my piano worth?

My piano was purchased 1978 at Evan's Music Center in Houston. It has the number 7389 stamped in an opening through the back plate. It is an upright piano and has a gold plate above the keys that says GRAND. I am looking to sell it and need to know what it is worth. I cannot find it anywhere online and would prefer not to get it appraised. Does anyone have any knowledge of this type of piano?