most you can find for 20k, the harder to get ones will be around 50k
The one from den of rancor, is 50k. Damp eyes i haven't seen in a long time.
All about supply and demand though. Some you'll barely get anything for, and i'm not saying anything will sell fast.
Actually the ones from Den (Wooden) are the cheapest because people get a lot of them while farming fire based blm scroll or clearing the area for a Haku run.
The most expensive are the ones the Mindgazers in Sea Serpent's Grotto drop (forgot the name) since there is a lot of effort required to get the one-time use key to their spawning area and to get to all of the spawn points you have to follow a one-way path.