The cost to replace a mailbox post ranges from $50.00 to $150.00 when you Do It Yourself and depending on the type of mailbox post you're replacing.
For a simple wooden Mailbox post the cost to replace the wooden mailbox post is around $50.00 or less.
You can buy already made mailbox posts made from 4x4 posts for around $50.00 or less depending on where you're at.
If you hire someone to replace the mailbox post then the cost will be a bit higher due to labor charges.
When hiring someone to replace the mailbox post it could cost around $100.00 in labor although it may sometimes be a bit less.
A good handyman should be able to easily replace a mailbox post if you're not up to doing so yourself.
Just make sure the mailbox is at the proper height and easily accessible for the mail person to deliver the mail.