They are all high. For your rear axle UPS ground is the way to go. It'll be a feather cheeper than Fedex. I don't think USPS can even handle it and DHL will leave it on someone else's doorstep. Freight companies are only good for heavier items, yours is right in that realm of being too heavy for USPS and not heavy enough to justify freight. UPS ground.
cheep cheep. honestly UPS is golden for anything under 70lbs but I think DHL is the way to go here. your buyer may have to pick it up at their local hub though. but they will be cheapest.
It would help to know from where to where. Check Greyhound, they'll throw it in the bay underneath the bus, it will take a while to get there but it will take the scenic route and will be cheaper.