I've heard of trip tags. Those are issued by the DMV to move your rig from one place to another without having to register it. Such as, moving a bus to your home so you can convert it into an RV.
In Virginia, if you don't have insurance, you can purchase it for $41 along with your trip tag at the DMV. Each state is different, and that's just what popped up when I Googled trip tags.
Something like that usually lasts for about 3 days, and I know people on here have used them. I would highly suggest taking the time to go down to your DMV, standing in line for several hours, and asking about this. Be very clear about what you're plans are for moving your privately owned non-commercial bus, and politely ask to speak to their supervisor if they don't know how to help you. Otherwise you have three options, as far as I understand. Your first option is to purchase an entire year's worth of insurance for about $500, possibly more to have your neighbor on the policy. Your second option is to find an insurance company that charges monthly, and then drop the policy a week after you get it, costing about $50. Your third option is to drive it home yourself like I did, sweating bullets the whole way, costing nothing.