Pictures would help. Those were sold in big quantities in the 1970s in both kit and finished guns. They were imports sold under many labels. When I had me gun shop I sold them very cheaply. They can be made to go "bang" but are pretty wuthluss for any real shooting at ranges beyond five feet. If it looks nice can make a neat thing to keep on your desk as a paper weight.
Depending on condition, IMHO, not more than $25.00. Tops.