your rates are so wrong. At 350X exp 1 dragon bone = 88200 (OSRS = 252 exp), so it's 150 bones for 99 not 500.
x350 (same as combat XP rate - 500 dragon bones)
x300 (603 dragon bones)
x250 (724 dragon bones)
x200 (905 dragon bones)
x150 (1206 dragon bones) (742 hard mode)
x100 (1810 dragon bones)
x50 (3620 dragon bones) (742 ironman mode)
your rates are so wrong. At 350X exp 1 dragon bone = 88200 (OSRS = 252 exp), so it's 150 bones for 99 not 500.