Check this: that's very interesting.
You can buy a speargun building kit that is basically a semi-readymade gun. The kit includes gun barrell with rail and hole for bands (all you have to do is shape the barrell), handle (grossly cut to shape your own custom), trigger mech and resin. All for 120 euro.
All you have to do is shape it and assemble. I think it's quite cool: it saves the hard part of the job (cutting wood laminates et cetera) and leaves to you the fun of customizing your own gun.
ARBABRICO |Arbatec