I just shipped 2 pairs of bucket seats with USPS. one pair was from a 68 Charger, low back buckets, these were just bare seats, took them apart and shipped them in 2 boxes, total cost with insurance and tracking was under $70.
The second was a pair of GM high back buckets with the seat tracks and hardware, these were more cause there was a spendy surcharge for the bigger box with the seat backs, shipping was $165 total for these dissambled, shipped in 2 boxes with insurance and tracking.
For me, it was definetly easier to ship them in 2 boxes, dissasembled. Besure to let the buyer know if you do this, then they can plan on putting them back together. BTW, both buyers were very happy with my shipping methods.
$160 seems to be the shipping cost on other seats on ebay, Greyhound would be cheaper but not all towns have a terminal so the buyer may have to travel, more of a convience thing just to have the US mail leave them on your door step.