You may have noticed Exhumers skill books disappeared from NPC skillbook venders with the mining changes a while back. Since then a few players have been buying them all up and reposting for obscene prices.
CCP has been utterly silent on the matter. They won't say if it's intentional, a bug, or even if they'll be back on vendors eventually. Nothing but complete silence.
The thing is there's absolutely no reason to pay these crazy prices since you can still direct inject the skill from your skill sheet into your skill queue. Simply open your skill sheet, go to Spaceship Command, drag the Exhumers skill into your skill queue and this dialog pops up:
Click "Buy Skill" and it only costs you 39 million ISK instead of getting ripped off for over a billion on the market.