Concrete posts are not hard to make.
1.
Cut a plastic pipe in half lengthwise.
2. Reassemble with hose clamps.
3. Plug the bottom end with a wooden plug with holes to hold rebar
4. Fill with concrete
5. Rod with a spare length of rebar to remove trapped air. (alternatively smack form with a hammer or vibrate it B_U_T don't get carried away as you don't want to separate out the aggregate from the mix.
6. Cap the top hole with a holed cap to hold the rebar in position.
Some additional thoughts:
1. Add a plasticizer water reducer to the mix to get a very mobile easy flowing mix without having to add extra water which will lower the strength.
2. Keep the rebar two or more inches from the outside of the form. (if you overlap/splice rebar overlap it at least 25 times the diameter of the rebar)
3. Don't put rebar near the center of the assy as that rebar will hardly do anything for strength/stiffness (bending resistance) Three or four rebar in triangular or square pattern is good. rebar position can be maintained by tieing with stiff wire.
4. Do the math... this is a 6 inch or larger diameter post.
5. you can put waterproofer in the mix if you want the post to last for your grandkids grandkids.
6. You can bore holes in the forms (right angles to long axis) and insert smaller plastic pipe to accept cables, sucker rods, barbed wire or ... if you want really neat appearance.
After the mix sets up sufficiently to not be harmed by removing the forms you remove the hose clamps and peel off the plastic pipe to reuse over and over.
Oh, the little pipes to make wire ways through the posts... they need to be split lengthwise on one side, not
cut in two like the big pipe. They can be driven out of the post with a drift and a hammer and reused.
Another nice touch is to add concrete dye to the mix and get a much better looking post.
Pat