I shipped a single front fender via greyhound express. I wrapped in a shipping blanket and then shrink wrapped it. It arrived safely but I feel like the fender's safety is in the hands of the bus driver.
Greyhound has worked well for me, but I put every item in a box. Bicycle shops are happy to give away empty boxes, just cut the to the size you need, a table saw works great for this. Bob
I to use greyhound but I put card board on the corners bobble wrap and then shrink wrap. But there could be a problem depending on where you are shipping to and how many times they change buses that is where the damage might occur.
Your going to find the cheapest shipping is Greyhound. I've shipped Cowls to Fenders and have not had any problems. I've had more problems with the counter people who do not know how to fill out the paper work or operate the computer.