DIY Fish Bonker?

Total fishing newb here so please forgive a potentially ignorant question.

What I've seen is that one of the most reliable and humane ways to dispatch many kinds of fish in a kayak without potentially stabbing yourself in the leg is to just give it a sharp bonk on the soft spot on the head. Looks like I could buy a club for the purpose for $10-20, but I'm also a student trying to minimize costs with a well-stocked DIY setup- can I DIY this with a dowel with a heavy bolt in the end, or something similar? Or is this one of those things where it's better to just cough up the cash?

I would sincerely hate to give a fish a good whack and NOT kill it, they've had a hard enough day as it is without the headache.   

I use the base of my gaff for bonking, although when I don't have a gaff even a couple whacks with the back of my pliers seem to do the trick. Cut the gills to bleed out the fish after as a secondary KO method...

Use something stout that floats.
It will have other useful purposes as well.
Wrap your braid around it to break off a snag.
My favorite, use it to hurl at annoying furbags to keep them away (hence the reason it must float).

This thread made me google "DIY Gaff" and I was quite surprised by the results.  Didn't realize gaff had another meaning, lol

On another note - it is silly how expensive some gaffs are. 

Ikejime.

It’s not a bonker you are after, it’s an ice pick,

my Scotty rocket launcher rod holder doubles as a rod holder and a fish bonk

Cut a closet dowel 22 inches in length, groove it a both 12 inches and 15 inches.  Not only a "bonker" but a means to quickly measure lings, greenlings and cabezons.

A piece of PVC pipe works OK for whacking small fish like trout, but doesn't have enough weight to subdue bigger fish. 

Use the end of your fishing rod, it's free 

An option to a bonker is a screwdriver blade or needle nose pliers in the brain.  Often easier than beating a fish, especially halibut.

 
  Find a small tree branch (Oak is nice)  cut it to a reasonable length and there ya go!

This thread made me google "DIY Gaff" and I was quite surprised by the results.  Didn't realize gaff had another meaning, lol

On another note - it is silly how expensive some gaffs are.

I've only made that mistake once 

An option to a bonker is a screwdriver blade or needle nose pliers in the brain.  Often easier than beating a fish, especially halibut.

A small screwdriver is the best. A stainless steel ice pick even better as it won’t rust.
Three advantages over a club are:
- small, lightweight, and can be stored in tackle box
- unlike the club, where you can accidentally hurt yourself, this is precise. You poke the fish in between the eyes, slightly up, to severe the brain.
- the blood won’t go into the meat, so flavor and texture are better

An option to a bonker is a screwdriver blade or needle nose pliers in the brain.  Often easier than beating a fish, especially halibut.

Yeah? I was worried about the accidental leg stab factor, but it may be that the stab is not as hard as I think it is.

I've found clipping the gills with shears and quickly placing in water kills a fish very, very quickly. 

Seems more humane than beating it with a club.  I've seen people bang fish over and over and they are still moving, not sure if they are alive or it's reflex.   I feel confident when the blood is drained the fish is dead.

I do also brain spike sometimes which is a sure way to kill as well, followed with cutting gills.