Is $3,500/mo for a 4-infant daycare reasonable?

This is expensive for daycare but on par with what you would pay for a nanny share which is quite standard here at $20 per hour, per kid. If they have a 2:1 adult to infant ratio, however, that's essentially the same as a nanny share. So it kind of depends what your preference is - if you prefer the baby to be at home vs. out of the house all day, if you want them socialized with more kids, if you want the additional help at home that sometimes comes with a nanny, etc.

For a daycare that does a 4:1 ratio of adults to infants (which is the licensing requirement) I would expect to spend more like $2500 on avg. 

Unfortunately I have found the very good daycares to be in that price range.  You are effectively paying for a nanny-share. 

I think $3500 sounds extremely expensive, even for the Bay Area. My now 4-yr old was in a home based daycare just over the El Cerrito border starting at six months old for less than half that (both my kids went there). And the fact that he continued there until age 3 when we switched to preschool meant continuity and fewer care transitions. I think you can find great home-based situations for an 8-mos old for less money.

The monthly fee is more than most home-based daycares charge by a large margin (perhaps even double what you can find in other home-based programs). However, the ratio is low, essentially 2:1 in a couple of months, and thus more similar to a nanny share. That rate wouldn’t be crazy for a nanny share. 

But, $3,500/month would be similar to the rate at a “nicer” Montessori school for a toddler, albeit with ratios higher than 2:1.

Seems expensive. We paid ~$1800 for a home daycare in El Cerrito a couple years ago for the same age/ratio.

This seems high to me, although the 2:1 adult to infant ratio is the lowest I’ve heard. Are meals included? What are the hours? Those components would influence pricing. Having toured many places we ultimately went with what felt right and have had no regrets.

My LO is at a small, in-home daycare (also 4 max and she started when she was 8 months). Hours are 8a-5p and meals are included. It’s in Richmond just over the El Cerrito border and is about $1,000 less per month than what you quoted. If you’d like any more info please reach out.

Lastly, (and not related to your inquiry) I’m wondering what infant-only means. Something to consider is if/when you would age out and have to switch?

Hi and welcome to the area!  I live in the area you mentioned and did not come across any daycares that expensive.  But I suppose it's reasonable if you can afford it (my family certainly could not).  There is a wide range in prices for daycares.  I think $2500/month is on the higher end so $3500 is definitely surprising to me but then again I know there are people in this area who are wealthy and would be happy to pay that amount.  Different parents prioritize different things.  For me cost/affordability was a big priority and I didn't mind that it was a larger home daycare (8 little ones). I looked at the licensing information online to see if there were any violations noted and felt very reassured by the reports from unannounced visits from the county.  I don't think cost necessarily correlates with quality as long as a place is in good standing with the licensing agency, has good reviews/references, and you as the parent feel comfortable.  

PS- if any of the other three babies have an older sibling in school, that baby is going to bring the germs to the daycare and it'll spread just as much around 4 babies as it would around a larger group!  So I'm not really sure there's a benefit for the babies/families in a very small daycare vs a larger one.