I'll jump in on the au pair option. Au pairs have been a godsend for us, but it's going to be very different from having a child in daycare. It's like hiring an employee and a roommate at the same time, and requires a good amount of interviewing, planning, and time spent training from the host family. Also, I think Australians have more flexibility with au pair hours and pay than Americans do, but even so I'd be surprised if having an au pair was cheaper than having a child in daycare 2 days a week once you factored in other costs, like room and board, extra car insurance, cell phone (we provide one), etc.
That said, au pairs have been a huge benefit to us (ages 6, 4, 1.5 and one due in January too), since my husband and I both work irregular hours. Having a third, reliable person that knows and loves our kids (and can DRIVE) has been amazing since we don't have family close by either. The cultural exchange has been really fun, and it's been a kick to keep in touch with these awesome young people after they leave our family.
Screening does take time and effort. Au pairs vary a lot in experience, but all of them should meet minimum experience requirements with children. (2 out of 3 of our APs have been European preschool educators with university degrees -- i.e., WAY more experienced than me!) What takes longer to suss out is what their lifestyle is like, maturity, and what their expectations of the experience are (and what yours are too.) Being upfront with any challenges in your life -- like the challenges of living with a newborn, house rules, etc. -- goes a long way in finding someone that will click with your family too. You'd be surprised at what many candidates decide they can deal with, so long as they know it's expected in advance.
One more thing: I would double check what your country's rules are regarding infant au pair care -- in the US, au pairs are not allowed to care for infants under 3 months on their own (though they can be in the house with them, so long as another caregiver is present.)
Good luck, and congratulations!