I recently bought some snails (Trochus and Bumble Bee) along with fish from Dr Reef Quarantined Fish, https://drreefsquarantinedfish.com/. All of their inverts are quarantined, but probably not for months. Their website says $60 for shipping, free if over $500. Most snails are sold in lots of 10 or 25. Gold Ring Cowries, however, are $20 each.
I have not had good success shipping USPS from Reef Cleaners.
I also bought snails a couple of times recently from AquaHaus in Springfield and was happy with them, but his quarantine process isn't as rigorous as Dr. Reef's.