600M on what planet?
I don't have a very good scope of this, but you should average 100-150xp per chin throw overall (more in the upper levels and less in the lower levels).
That said, I'll oversimplify and give you a 13M xp figure for 55-99 (not that far off).
13,000,000xp / (125xp / 1 chin) = 104,000 chins.
~1,500 chins can be thrown in an hour, so you'd take 69 1/3 hours (4,160 minutes) to throw all of those. Assuming a relatively easy to obtain +20 prayer bonus, you'll be draining prayer at a rate of 12.0 points per minute.
4,160 minutes * (12.0 points / 1 minute) = 49,920 points.
At level 43, a prayer potion restores 51 points (17 per dose).
49,920 points / (51 points / 1 potion) = 979 potions, three-dose
At level 70, a prayer potion restores 72 points (24 per dose).
49,920 points / (72 points / 1 potion) = 694 potions, three-dose
So, in summary, the costs at current prices for:
43 prayer: 979 potions * 8,500 GP + 104,000 chins * 700 GP =
81.1M
70 prayer: 694 potions * 8,500 GP + 104,000 chins * 700 GP =
78.7M
Note that I may have overestimated the number of chins you'll need, but these should be relatively decent estimates. Hope it helped!