We use aluminum posts on most of our post and panel signs.
Occasionally pvc sleeved pt posts.
You can buy 24' lengths of 4" sq 1/8" wall tubing for $4.50 a foot and cut to length as needed.
It's not hard to paint.Etch prime and topcoat.
We find it more cost effective for everyone to use alum.
Think about this by the time you pick up the posts,make sawdust,dress them to look nice,handle them and get splinters you spend a least a day doing this for a nice set of posts.Ask yourself if you would be willing to spend an extra +- $50 bucks to make that hassle go away.
If you use alum you can cut your time way down and you have a nicer post.Well worth the extra $50 bucks the alum cost you.
We even use it for cheap real estate signs.
Here is one we just did.We used 4" sq tubing and welded the frame together then vhb'd the flatbed printed acm faces to the frame.
Transported to the jobsite in one piece.Dug holes and dropped it in.
We could have used wood but we try to work smarter not harder around here.