my mailbox was hit by a vehicle so I decided I wanted to do something creative/different but also didn't want to spend much money as it may just get taken out again in the future :)
this is a good project to get kids to help you with
instead of cutting into the concrete easement, I installed 2 post bases & locked them with sleeve anchors. They're sturdy enough but will give if hit again. drilling the holes for the sleeve anchors was the hardest part of the project.
I used a left over 4x4x8 for the posts, scrap 1x4s, 1x2s up the sides (1/2" gap between boards), and a 2x4 scrap to attach the mailbox. I eyeballed the width between posts using the mailbox itself. I left over stain from another project (almost bought a quart of oops paint at HD)
I figure the total cost would have been about $100
It's a super easy project that took about 4hrs. I've already had a couple of neighbors come by to take measurements to try something similar.
FYI: USPS guildlines for installing a curbside mailbox: https://www.usps.com/manage/mailboxes.htm