Habibs Hens, what a beautiful way to remember your son.
I've never cremated a chicken, but... when my pet rats die, rather than pay the $150 charge I take a large unglazed terra cotta pot, put a piece of tile in the bottom to plug the hole, and build a fire in our backyard fire pit. When it gets good and hot, I place the rat in the pot (I put the body in a paper bag - makes things easier) and put the pot in the fire. It takes about three hours, and there are usually some bones and teeth left. After everything cools, I pour the ashes into a decorative urn that hold the remains of all the rest of my lovely ratties that have passed on. When we one day buy our retirement house, I plan to put the ashes in a flower bed and have a small marker.
One more idea - I've heard of people using an old lidded stainless steel or cast iron pot in the same way as I used a terra cotta pot, that they reserve just for cremations. The terra cotta pot usually cracks, so that might be a better idea.
It's been really interesting reading about different peoples' practices and attitudes when they lose a beloved pet.