Unfortunately, you're not going to get an exact answer here, because everybody's lifestyle is slightly different. However, you can guess what's going to be the big changes in your budget. I think there will be 4:
1) Your take-home pay will change. Use a calculator for you exact number, but according to [1], a single person will take home about $6,400 / month.
2) Unless you live in Manhattan, your rent will dramatically increase. Like everywhere, there's a huge range. Want to live in Oakland with a roommate and bike to BART? You could probably find $1,500 / month. Want a new construction 2 bedroom downtown or close to Caltrain on the peninsula? $5,000 / month. Houses can easily run $8,000 / month with mortgage + taxes if you can scrape together the $300k down payment. Look around on Zillow and ballpark it.
3) Eating "nice" food out isn't cheap. There's plenty of good, cheap eats, but if you're thinking date night, it's easy to drop $120 for 2 people then go off and order half a dozen $8 beers. The high end is really bad --
there's a bunch of amazing restaurants that are $75 - $100 for 6-8 courses. If you're moving from a small city, these simply don't exist. This might be a shock if you're used to eating at "the best place in town" for a special occasion.
4) Depending on where you are in life, there's a bunch of family-ish things that can really eat up a budget. Dog walkers are $20 / day. Infant day care is $2,000 / month. Getting around is kind of a pain if you don't exclusively live, work, and play in the city, which can be fixed by giving Uber $25 / ride. And unlike other cities, there isn't anything that's remarkably cheap (e.g. when I lived in VA, groceries were like half the price I expected. It was great.)
Ultimately, though, a lot of people make it work. The networking and career attitudes in tech are unmatched (I moved from Boston at age 30), the weather is great, and it turns out that a bunch of my friends who I thought had disappeared had just moved out here and they all hang out.
If you're just in it for the money, it's a close call. Your best bet is to work out here between age 22 and when you have kids, then move somewhere affordable with the $5mil you made during that time. But that's not exactly why I moved here -- I've learned more in the last 2 years than I thought possible, and I've fundamentally altered the arc of my career. I may leave at some point, but I'm glad I moved out here.
[1] https://smartasset.com/taxes/california-paycheck-calculator