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)
Voted x150 but x100 would be cool too, seeing as bones will be the first item sought after in large quantities and I think it'd be a good start to a proper economy.
Also; are you gna add wyvern and dk bones for prayer training?
I'm gonna be realistic now. I don't think requiring 1.2k bones to get 99 prayer is healthy for your game. I don't think many players are going to be attracted here knowing they'll have to collect 1200 bones for 99. Especially when you consider a lot of people will reset stats.
It's already going to take about 7 hours to get maxed in other stats not including prayer. So prayer should have some difficulty to it. Rates for combat are similar to the very first bs1, and on there it was about 870 bones to 99. Not saying I want that, I'd prefer maybe 400-600.