If you already know you want a rifle, buy it now, in Utah. Don't buy it in California.
If you want an AR in California, buy a lower in Utah, not in California. Then order the other parts on-line, out of state, to save sales tax.
In California, you have to pay the FFL a minimum of 25 bucks as a "transfer fee" even if you buy a new gun from the store's shelves. Few Internet vendors will sell to California now, due to extra requirements for FFL transfers that are a PITA and cost the dealer precious time, and if they do sell to California, good luck finding a transfer dealer in coastal Nor Cal who won't screw you HARD for doing the transfer ($100 is not uncommon).
Then, you will pay between 8.25% and 9.25% sales tax in Monterey County, depending on the city where a store is located. Don't bother going outside the county; 8.25% is low for California and you can't do better (e.g. San Francisco is 9.5%).
Californians are so used to paying all these fees and taxes, they don't even think of it. But of course, they add up. It would be hard to pay as much for a gun in Utah, when you add it all up, as you will in California, even if the gun is "on sale".