Our insurance covers well-baby checkups at the appropriate times 100% including vaccinations, so that's been nice. I EBF until 6m, and we've started subbing in formula once a day so his dad can hang out with him. Formula (Similac organic) is $25/month.
I subscribe via Amazon for diapers, so a box of the fancy-pants Pampers is $38/month, and I supplement with cloth as needed. We buy a box of Costco wipes every other month for $20, so about $10/month.
I make about 70% of our baby food out of fruits and veggies we have anyway, but let's say I spend another $30/month on pre-made baby food.
Our crib/mattress was a gift from my parents, as was the second-hand rocking chair. We've been gifted a jumperoo and a walker thing (we're in a one-story apt, so no stairs), a swing, a jogging stroller, two diaper bags, and tons of new or hand-me-down baby clothes (and when my son outgrows things, they go on to other friends with younger kids). We paid $200 for a dresser instead of a changing table with an eye for his future, and our stroller/car seat "travel system" was $300 (Chicco KeyFit 30). The kid is an inch away from outgrowing it, so it'll be another $100+ for a convertible seat that'll fit him for the next 40+lbs. Our monthly output for toys/clothes/incidentals is probably $30.
I'm in grad school full-time in an online program, with two quarters left. I stay at home with the kid, so no childcare-- but when I finish, I'll probably volunteer based around grandma-offered childcare hours, because childcare would run as much as I'd make temping until I find a FT position in my field.
So roughly, without equipment, I'd say we spend approximately $130/month on the kid, not including paying off the $4500 in medical bills from pregnancy. Never let anyone tell you that it's easy or cheap to have a baby-- even with good insurance, it's expensive. I love my dude to pieces, but my husband and I took 10 years before we felt we were emotionally/financially ready, and I'm very glad we waited. I wouldn't have had the patience I have now if I'd gotten knocked up at 20 like half my friends from high school.