what is the age of the house?

It's often possible. We did it years ago to our 1952 rambler. But no one can answer your question on this forum: you need to have a structural engineer take a look at it.

It’s a 600-800k proposition around me for people that have priced it out recently, but i’m in bay area so everything is expensive here!

Maybe, but maybe not.

I looked into this once at one of my other houses, and it was just not feasible. In that situation it was of truss type construction, and really difficult to go up with another floor. Had I done so, the construction would have also been intensive, really having to move out, and everything in the house moved out, until construction was done due to it being exposed from the amount of time the roof was compromised until another living level and roof could be added.

But if your foundation can support it, then it's worthwhile to do as you do not need a foundation, and plumbing and electrical can be easier to do as well. If you live in an area that has building permits, that may be easier to get too, or at least less of them to get. So, it is pretty attractive to consider, and really should be considered as there are some considerable savings that might not be readily intuitive.

In my case it was just easier to add on. The building permit to add on was $20, I had plenty of acreage, and disruption was less. Once 100% of the construction was done, with all the dust and debris isolated from our existing home, I removed the back door, cut it a little wider to make it the width of the hallway, and suddenly had a 60% bigger house. That saved 9 months of disruption to my life which was well worth the savings I had by having to pay for a foundation.

But that was that particular house, and in that situation; that may not be the case for you of course.