"For example, if a druid trains from level 19 to 20, where does that 80 GP go?"
Consider a level 19 druid's ability to find whatever herbs and/or mushrooms they might need to open their mind to level 20.
Wait, there's someone who has a *better* ability, and the level 19 druid would pay that guy 80 gold, rather than hand-pick their OWN vision-inducing plants?
...well, I guess a level 18 Bard or Rogue with Expertise, could have a higher total modifier to their Medicine check, than a level 19 druid. Hunh.
Drugs.
Consider a level 19 druid's ability to find whatever herbs and/or mushrooms they might need to open their mind to level 20.
Wait, there's someone who has a *better* ability, and the level 19 druid would pay that guy 80 gold, rather than hand-pick their OWN vision-inducing plants?
...well, I guess a level 18 Bard or Rogue with Expertise, could have a higher total modifier to their Medicine check, than a level 19 druid. Hunh.