At 9 + months it was on average of 20oz of breastmilk every 2 hours, except at night... and there was a midnight-1am session (which worked out great, because I went to bed (and still do) around 2am.
I had a massive infection that killed my milk supply between 9 & 10 months. As in no more, buh-bye, life threatening infection, super fun. :P Which made formula rather necessary. At that time he was drinking 1.5-2 premixed 32oz cans of liquid enfamil lipil. Oy. Talk about pricey. 20-40 bucks a day in formula. (He would NOT take powdered formula). And he kept pretty similar to his nursing schedule of every 2 hours in the daytime, but he woke more at night. (9pm, 11pm, 1am, and o'dark thirty). So he was definitely getting better nutrition when he was BF'ing.
At a year, he started inhaling table food (he ate approximately half of whatever I was eating), and his formula needs got cut in half. He still woke several times a night to eat.
I bring this up, because losing my milk (aka unintentionally weaning) was a HUGE dent in our pocketbook, and reeeeeally changed how much sleep either of us got in one stretch... and so are things to be considered as you contemplate weaning.