Airut bones are associated with the Prayer skill. They are dropped by Airut. Airut bones give 132.5 Prayer experience when buried. This is increased to 463.7 experience when using a gilded altar with lit burners or 530 experience when using the ectofuntus.
This table can be used to compare and decide on how to train with the bones for the most desired cost versus experience gained. Notice how the cost in coins per XP point varies greatly depending on how the bones are used — but also remember that the different methods have different training speeds.
A player choosing to use airut bones all the way from 1-99 Prayer, using a gilded altar with lit burners and no other experience boosts, would, if all the bones were bought at the current medium price on the Grand Exchange, spend 247,645,756.11.
Additionally the first bone used would take them straight to level 5 Prayer.
Using the ectofuntus would cost 216,666,673.79, but would take far longer to do. Simply burying the bones would cost 866,666,695.17.
After an update, airut bones were physically increased in size, to better match the creature they came from. Prior to the update, the bones were similar to the size of regular bones. This update made the bones occupy a 3x3 space. This is odd considering that much larger creatures, such as General Graardor, drop bones which occupy a 1x1 space.