At least in California, you're nominally allowed to self-insure your car, but it's rare and not an especially good deal: your options are traditional insurance, a large cash deposit (in the tens of kilobucks) with the DMV, or a self-insurance certificate that's usually only given out if you're managing a large fleet of vehicles. There's also the option of a surety bond underwritten by a non-insurance company; how good a deal that is depends on who you're negotiating with and I don't know what your options are.