Clair,
Your vet is a keeper! Sounds like he's doing it at next to cost. I spend $20 for overnight air from VA on USPS. The ACTH plasma must be frozen immediately from the centerfuge, shipped on ice and received frozen/verycold. Schedule the test early in the week so it can get to Cornell before they close the lab. You sure don't want it sitting over a weekend thawing!
Mandy