Mrsy, i understand your dh's concerns to a certain extent but a huge part of me says 'well he's had 9 months to realise that finacnces were going to be stretched and to sort something out'
a baby, expecially your first, is still so new and precious for those first few months i really can't see how you could walk out to work and leave her with anyone, even a doting mil. it takes so long to acclimatise to becoming a parent and get used to this tiny person you've brought into the world. trying to settle at a new job when you're still in those early days of motherhood strikes me as something practically guaruanteed to set off PND and make what will already be an incredibly tough time almost impossible to bear.
keep in mind as well, you may have a baby who's starting to settle by 6 weeks old...... or you could have a baby that doesn't sleep, screams constantly and feeds round the clock like i had first time round.
how in the name of god would you function in a job with 2/3 hours sleep a night and no down time at home whatsoever? and would it really be fair to ask your mil who has already done her duty as a mother to take on a diifficult newborn?
and what about feeding and nappies? the best way to save money for the first few months of a babies life are to bf and use reusables. i doubt very much you could establish bf-ing to the point of expressing enough for a days work 3 days a week within the first few weeks (i could never get to that point) so you'll have to switch to ff. whatever about the emotional cost of switching if it's not what you really want at that stage.... has he checked the price of formula recently? and the cost of bottles, teats, steralisers, elec to run steraliser and all other related costs of ff? and has he seen the price of nappies recently? asking a minder to use reusables is a big ask and his mother simply may not be willing to do it.
i wasn't ready to leave my dd to work until she was 8 months, and even then i was only leaving her with dp for a few hours a day and it still broke my heart, up til that i did some catalogue work which meant i could bring her with me doing drop offs and collections to make neds meet, dp lost his job when she was 5 months old and we were very broke so please don't assume i don't know exactly what you're facing, i just don't think you going out to work within weeks of having your little girl is remotely a solution.