I believe you answered your own question. When there aren't many individuals left in the world with the associated expertise, and when a younger developer sees

I believe you answered your own question. When there aren't many individuals left in the world with the associated expertise, and when a younger developer sees no growth potential for learning this expertise, you probably will have to pay more a la supply & demand. That said, this doesn't seem particularly high. My guess is a migration would easily cost seven figures. However, sometimes delaying the problem is really kicking the can down the road to when there are even fewer people with lotus expertise.