I used to live there, so I feel sorry for you folks. Whatever you do don't just let it go unpaid. I had a small trailer that I bought for a move. The yearly fee was about $25. After I used it I put it away and forgot to pay the next year. I hadn't given the DMV my change of address for it so I didn't receive a bill. About five years later a friend wanted to buy it but I had to get the registration current to be able to sell. With the unpaid fees and penalties the price to get it current was over $800. For a $200 trailer. Ended up bringing it with me to Colorado, cost $11 to get square here.
About two years before I abandoned CA a number of years ago, I knew I was outta there. At the time, registration on my Mustang and two motorcycles was something like $800/year and going up!
I said "to hell with that; I'm moving anyway" and just registered the smallest motorcycle for something like $80. Then I just moved the sticker to whichever vehicle I was driving at the time, until I finally got the hell out. Saved about $1,500 and my new state didn't care a whit that everything was expired once I got here.
Considering how much Kalifornia stole from me over the years I was there, it was small payback.
Now, for a GMC Jimmy, two motorcycles and a trailer, I pay something like $220/year. And that includes vanity plates on all but the trailer.
It's fun watching Kali decline now that I don't have to be there to shoulder it. The trick now is to keep those fleeing from screwing up the other states.