heh, i gave o'aka 10,100 gil for some reason....it was worth it though. a potion is 35 gil
heres why:

Investment Total:..................Price:
0-100 Gil.............................. Standard Price x2.0
101-1000 Gil.......................... Standard Price x1.5
1001-10000 Gil...................... Standard Price x1.2
10,001 Gil and Up................... Standard Price x0.7