US city guide to low rents
The best way to find an inexpensive place to live varies from place to place.
The local craigslist is mostly populated by apartment finders whose fee gets tagged onto the rent. Expect to pay 10-15% more if going this way. The best way is to find out which neighborhood you want to live in and walk around looking for "for rent" signs posted in windows.
A good strategy for cheaper rents is to look near the terminus of the L-trains (consider purple, brown, blue, and orange). Here studios and 1bd apartments are generally in the $600 range (this typically includes some utilities). In River North (the most expensive part of town), 1bd room apartments cost down to $800/month. Coach houses (converted garages) often go for $600+utilities closer to the loop in areas like Pilsen.
Good deals vanish quickly (within 1 day) so be prepared to act fast. Consider bringing a check book and offering to sign the lease on the spot if you see something you like.
New York City Metro Area
Although there's a high average cost of living in NYC, there are places where good housing is available for a discount. Notable among these are Harlem, Hoboken and Jersey City, all of which suffer from a bad reputation that directly impacts rent prices ("Jersey? Ew!"), but which can be safe, convenient locations. Other cheap locations are the Bronx (dicey) and Astoria (immigrant neighborhoods).
When renting, you always want to check for broker fees and avoid when possible. The renter pays the fee, and it's typically one month's rent. That increases the rental price by 8% if you stay for a year.
Jersey City is walkable, has nice neighborhoods, and has reasonable rent downtown. You want to rent brownstones via Craigslist, rather than apartment complexes which charge a premium. This area is bounded by highway 78 (NJ Turnpike extension) on the west and north, the Hudson on the east, and Liberty State Park on the south. Typically, a one-bedroom in this area will rent between 1100 and 1800, depending upon amenities. Transport into downtown Manhattan is 8-12 minutes by PATH train from Grove St/Exchange Place. A comparable apartment in Manhattan proper is probably about twice the cost.
Further out in Jersey City, Journal Square has some nice locations, but it can be a bit dicey. Rents are much cheaper but there is more crime. It's recommended to check this area on a case-by-case basis to see if you feel comfortable.
Orange County, California
This is a high-rent area and there's no way to avoid that entirely. There are marinas along the coast, but they seem to have long waiting lists and cater to wealthy yacht owners and ban or discourage liveaboards. There are a few RV parks but the ground rent seems expensive relative to renting a room or small apartment. Inconspicous parking is abundant so this could be a good place to live in a mobile stealth RV. Otherwise, you will probably need to find an inexpensive apartment.
In general, rents are lower in immigrant communities, for example the Mexican neighborhoods in Santa Ana or Vietnamese neighborhoods in Garden Grove. The grocery stores in those neighborhoods tend to have better prices on staples and produce, too. Also, there are a few old walkable neighborhoods, mostly clustered around the train stations. Many people here take on boarders, so renting a room is an option. Rooms without their own parking are cheaper, which could benefit a carfree person. It's also possible to buy or rent a house and rent out individual rooms to defray costs.
A very expensive area so consider alternative possibilities. RV parks are generally $600-$700 for a spot depending on access to BART. Towards the ends of BART in the north and east bay, RV park rents drop to $400-$500.
Marinas are cheaper ($400-500 for livaboards) but there are big waiting lists of 1-2 years. Another popular solution on the peninsula are room mates. If you don't mind all of them being software engineers or working at google or NASA, there are many such "hacker houses".