The Bay Area.
Full disclosure, I have only been to the Bay Area 3 times. About 2 weeks at a time.
I lived in my truck camper. I thought it would be doable to stay more long term. I have a refrigerator, stove, sink, table, bathroom, and queen sized bed.
You would need to identify possible places to park. I can tell you that there is a GREAT place to park in Alameda, on top of the tube from Oakland. This road is very wide, and can't be devoloped since it is on top of the tunnel. There is an RV parked there... with a guy living there... every year (I think the same one)
You will also be able to find somewhere near your work. Look at google maps, drive around. You need to identify a few places like this:
Residential area. On a corner. With the house facing a different direction. You want to park on the side of the corner, next to the side yard.
Now, find as many of these as you can. Make sure to locate them in different cities. Because if the police hassle you... You need to leave their area. The police won't arrest you. They will simply say you can't stay here. Just agree and get in and drive off. I "save/star" Them on google maps.
Once you are working, inquire among co-workers... You are looking for a driveway, or just on the street, where you can park, with their permission. That adds to your list of possible parking.
You can get a gym membership, hopefully to a place with a number of locations. Even if you get a camper with a shower, it is too much work to get water, and empty the grey water, etc.
Or shower at work as others have mentioned.
South bay area is better than San Francisco. More spread out and laid back. SF parking is not as level and there are more restrictions. Also good, north in Marin county and the Oakland side.
A truck camper can be bought for plenty cheap. You don't need a shiny new one. You don't want one with a slide. Also no pop-ups. Shoot for an 8 foot, or 8.5. Maybe a 9. You are being discrete. For driving around, you don't want a huge overhang, harder to park etc. I attached a picture of my unit. I drive this 30,000 miles a year. In every situation (Manhattan, Seattle, SF... it is not that bad) there is 2 of us living in it. So with one... you will have more room.
Check out
http://sfbay.craigslist.org/sby/rvs/5289143294.html $3500. Very nice condition. Along the lines of what I would be looking for.
Get solar panels. They will cover your electrical needs. I like the 327w SunPower. Or any high output grid tie (cheap) panel, or if you have the room on the roof, panels. Use an MPPT controller and a couple batteries. Even in the bay area this will keep your computer/cell phone charged... and propane heat running. The small area of the camper makes for a very frugal heating arrangement.
You may find a bike is a good idea. Depending on the parking at your job... it might be tight/underground etc.
If you don't have a pickup yet... you could look in to other options. Mostly based on the Sprinter van, or something of the like.
Assuming all that... your expenses will look a bit like this,
Gas, $~50-100 a month
Propane, $20-80 a month, average around $40 (assumes you like to cook and bake, etc.) Also will be higher in the winter, less the rest of the year.
Auto insurance for the truck, Plates, etc. No insurance/plates for the truck camper, unlike a trailer/5th wheel.
Everything else, entertainment/dining/etc that you would normally do.
You will want internet, I would suggest the T-Mobile unlimited data plan. You get unlimited data on your phone, with 5-7GB of tethering. Coverage will be good in the bay area, and I find the speeds pretty good. Last test was 32mb/20mb up/down. It is a $30 option on top of the regular calling plan. We have 6 phones @ $25 each unlimited calling/text... plus the $30 data on mine. Total $55/m. If you need more tethering data (although large downloads I just download on the phone and transfer) they have that as well. It is really the best deal at the moment.
It is also possible to rent a room. Looking on CL, plenty of options in the $1000/m range. Some $700 ish as well.
Anyway good luck! I have been doing this all my life. If you have any questions/things I missed... message me.