How can aspiring actors to survive in la?

Actually the vast majority of aspiring actors don't survive in LA and give up and go home after a year or so.

And yes they do start with thousands of dollars in the bank when they move. LA is an expensive city. Rent is about $1,500 a month (and you'll need first and last month's rent to get anything.). You need a car in LA, especially if you're an actor wanting to make auditions - gas, maintenance and parking add up. And quality acting classes are not cheap and professional head shots are important. So even if they have thousands of dollars in the bank they're going to work at bars and hotels if the jobs give them the flexibility to attend auditions and slows the drain on their savings.

Most actor's who are in it for the long haul have an "along side" job - contract work or freelance work that provides the flexibility needed to work on an acting career. I worked as a technical writer, grant writer and public relations writer. I had a friend who was a personal trainer. You can register with a temp agency, do promo work or modeling (acting and modeling are two different careers), and there's catering, web designer, personal assistant work, tutoring, babysitting or pet sitting, dog walker, video taping/editing (like graduations, weddings, etc). Get a real estate license and work as a real estate broker. And any combination of the above can work. (Of course if you're not a US citizen you need the necessary work visa/green card to legally work in the US. And generally speaking nursing is not a really flexible career.)

And then you reduce your expenses so living with roommates, not eating out or going out to clubs, no vacations, buying things second-hand, learning how to do your own repairs, sometimes bartering for services.

And make smart investments - don't fall for scams and rip offs to find short cuts to an acting career. Know the business end of things so you can make smart decisions.

Good luck.

They spend the money they earn on their aspirations not on things like food, nights out, holidays, etc.

They don't get their own place and often not even their own bedroom. It's not unusual to find 3 people sharing a studio or 4 people sharing a one-bedroom apartment. You need at least $10,000 minimum saved up before you move to cover the cost of your rent, car, acting classes, and supporting yourself until you find a job. There is a lot of competition for waiter, bartender, etc jobs so it might take you 6 months to find a job
You don't go out to eat, you don't go out drinking, you cook at home and cut down your expenses as much as possible
When I first moved to LA we were 3 people in a studio. We removed the dining table so the dining nook became my "bedroom" with a mattress on the floor and a sheet tacked up for privacy. We then had a sofa bed that one person slept on, and a twin mattress on the floor against the wall for the other person. From there I moved into a 2 bedroom apartment shared by 6 people - 2 in each bedroom and 2 in the living room. Everyone who lived there was an aspiring actor, model, comedian or singer. This is typical in LA. Most people you meet who don't have money are in share situations like this. Don't expect privacy or quiet. But the advantage of living like this is that if you end up with a good group, you help each other try to find work

Unfortunately even actors who are fully-trained and who are getting loads of audition still have to have another regular source of income.
The most that a typical actor will ever get is about 2 or 3 weeks’ paid acting work a year. That’s the average, and it will be in small roles, in small productions, at minimal rates of pay.

Most of the actors I know have free-lance jobs which they do self-employed virtually every day, every week all years round, so it leaves them free to take time off for the occasional acting job, rehearsals, auditions, etc.

They have such jobs as eBay traders, aromatherapists, proof-readers, children’s entertainers, photographers, copy-editors, writers, website designers, hairdressers, chiropodists, drama teachers, home-based secretarial services, researchers, singing teachers, cartographers, jewellery-makers, ceramics workers, researchers, kids’ tutors, dance instructors, personal trainers, etc.

And as Katrina says, most aspiring actors quit after a very short time, as they can never afford nights out, new clothes, etc, and because as Empty says, they spend every spare penny on furthering their training and experience.