My cousin does something like this as well. I do not, I'm a full-time engineer, family breadwinner, and a homeowner. We talked about our respective budgets a few months ago...they could not be more different. He doesn't have
any of the major line items on my monthly budget, which requires on the order of $2,500/mo at a bare minimum, which is easily met by working for 40 hours a week and drawing a dependable paycheck. He does odd jobs, usually various forms of graphic design with Photoshop or Illustrator - making up new menus for a restaurant, logos or website headers and design elements for a small business, T-shirt design for a church retreat or sports league, photoshopping a portrait for someone's anniversary, anything where you'd want someone 'artsy' but don't know who to call. A job might be between $50 and $500, the jobs and contacts come and go. Sometimes he's busy day after day, sometimes he'll go weeks without a job.
Weeks without a job, I say! How do you survive? Well, he sublets from a couple friends, but isn't on the lease himself; he usually keeps a month ahead of rent but sometimes can't find the money and will 'get behind', they're generally accommodating; moreso than a bank. He has no mortgage, no car, no car insurance, no car payments, doesn't need a line item for gas and car maintenance because he doesn't drive or commute, doesn't have expensive hobbies, has no cell phone bills (uses a prepaid phone that he tops up and uses as needed/as budgets allow), internet is part of his sublet room, has no TV, no garbage/recycling bills, no lawn care or other services, no home insurance...Critically, he has no health insurance - which sucks come tax season and would really suck if he wasn't a 25 year old in fine health who thinks he's invincible. Relatedly to being an invincible 25-year-old, he has no IRA or 401k.
Groceries cost about $200/month, his sublet of one room costs about the same, he doesn't have any other dependents, and if you don't want them there's not really anything else that someone needs to buy. To hire any professional for much of anything costs about $500, in a big city that's basically the minimum price of a day or two of skilled labor. If he can get one job that will pay him that much in any given month, his minimum budget needs are met.
Someday, he says, he'll want to move out and settle down and start on a career progression, but he's tried the 40 hour wage slave model and loathed it, and his lifestyle in the big city is fun for now. If by "big city living" you mean all the budget items you'd expect of a homeowner in a small town, but scaled up to downtown living by means of a 6-figure salary, no, this lifestyle won't pay those bills.