I totally understand! This is the same situation we're in. I took 12 weeks with my daughter and with this baby I'm taking the max, which is 16 (12 of which are unpaid, the other 4 are paid at 70%). We basically have our finances under really good control and once we're out of the first trimester (when everything goes out the window due to me being sick plus having to have some work done on our house) we just focus completely on putting money away. Like, that is seriously all we do. First my husband and I sit down and talk about it, why its important, how much of a priority it is, ideas for how to do it, how much money we think we'll need, ect. Then I do some spreadsheets and some math, and then we figure out how much we have to save every month. If we're coming up short, we start getting creative and figuring out other ways to cut back that maybe we didn't notice before. We have no high interest debt, so the debt we do have, we just pay the minimum until after I go back to work. And if we find at 10 or 12 weeks postpartum that we don't have enough, we will take a loan from my 401k. But that is our back up plan, just in case something goes wrong
When I brought this up with my husband the first time around, I didn't talk about the loss of money first. I talked about how wonderful it would be for me to be home and how good it would be for the baby, ect.
Oh, and my daughter is not in daycare, so the only money we actually save by me not working is the gas to drive to work. But I found that since I go out to avoid getting stir crazy, we spent about the same on gas.