Speargun for sale or trade

I've had this Canon speargun since I was 15yrs. old. That makes it late 70's early 80's model. Great working condition and just needs new line and bands. Whats this worth? ( spearos input welcome here). I'm thinking $40?? Will possibly trade for something kayak fishing related. Thinking it would be a good starter gun for someone just getting into diving. The gun is about 48" as well as the shaft too. I really don't have a need for this any longer.