One thing that costs us, in my first pregnancy and now that I'm pregnant with DC2, is food, especially in the first trimester. At the very beginning I felt the urge to buy all organic, free range etc and couldn't stomach anything that wasn't high welfare - now I agree with high welfare anyway, but couldn't always afford it before, so that was a change! But also because, almost inevitably, you may find one day that you can't stomach what you loved before and you must have item x stockpiled. Or you think you have everything possible in the house, but you just can't bear any of it and want to get food out/takeaway in that moment.
For example, normally I just drink tap water and sometimes weak squash. At the moment I am living on Sprite and 7Up
I know it's not great, but it's one of the few things keeping sickness at bay, I need the fizzy lemony-ness. So obviously that costs more, especially when I run out and need to buy some not on offer or from a local shop. My fridge is also currently full but just looking at it makes me want to gag (yesterday it was fine), so I've just ordered takeaway as the only thing I can think of eating right now is Chinese...
What I'm saying here is, save up some money for you for these impulses, cravings, aversions etc. It makes a big difference to how you feel if you can freely pick up the thing that helps you not feel sick, or the only thing you can stomach, without worrying about blowing the grocery budget.