Part of me thinks this should be under Guides, but, seeing as sell prices don't usually match their return prices (and I think Blizzard might fix this if people started exploiting it), I'm going to guess it's an exploit.
Basically, the Garrison Blueprints from vendors sell back at their original prices. They are Unique, however, so you can't transfer more than one of each one.
10x Small lv2's = 7,500g
5x Mid lv2's = 5,000g
5x Large lv2's = 7,500g
4x Auxiliary lv2's = 4,000g
Total = 24,000g
10x Small lv3's = 10,000g
5x Mid lv3's = 5,000g
5x Large lv3's = 5,000g
4x Auxiliary lv3's = 4,000g
Total = 24,000g
Grand Total = 48,000g
Just buy 'em all, server xfer, and then vendor 'em all.
Most people probably can't actually unlock all 48k of blueprints, especially this early in the expansion, but 24k is available to everyone and 35k should be possible to most. That saves some time from buying an extra Vial or other mount, allowing for resale later without the hassle.