First off, results (and registration amounts) may not be typical. I'm writing this in as much to advise future Opponauts who might find cause to be moving to the fine land of California for whatever reason it is one might find to move here (a love of wildfires, active fault lines, and bears perhaps?).
My one take away from the registration process, and the one I offer here is, if you're moving to California and your car can make it from where you are to where you're going and last you, don't get a new car before coming to California.
Sure, in all fairness you might (maybe) be able to get the car cheaper where you're at but what California does is levy a little something called Use Tax on "tangible personal property" - like say, a car - at the time of registration charged at the current going rate as if you bought the vehicle within the state of California. This is applicable, from my reading anyway, upon the registrant's property if the car is registered in California within one year of being purchased.
As far as I can tell, this is to dissuade California residents from fleeing their state to purchase tangible personal property. Couldn't possibly imagine why they'd want to do that.
In all fairness to California, they do cut you some slack and they count any taxes paid at the original state/place of purchase of the automobile towards the Use Tax being charged. Still, even with the monies I already rendered to the state of Alabama (my previous place of residency, which I am told was awash in blood and tears, filled with anguished wailing and the gnashing of teeth after the latest college football season), my combined state and city Use Taxes for car registration came out to around $510.
Now, as I said in the first paragraph, results aren't typical. If your state or whatever charges at or around the same tax rate as California at time of sale, you shouldn't see Use Tax. If you're coming from a state that doesn't charge as much sales tax as California, prepare yourself.
For the curious, the rest of the nearly $700 in that registration cost came from the actual registration fee ($43), vehicle licensing fee ($84), CHP fee ($23), what I believe to be a new registration origination service fee ($19) and a whole slew of other fees ranging in cost from $1-6 ($13). Total fees due, plus Use Tax, $689.
Also the front license plate I now mount to avoid bored cops dinging me with a fix-it ticket makes my GTI look off. I'm not entirely sure if I'm more annoyed at that or the money.