I bought pre-fab granite for my sister's kitchen in Sacramento and paid less that $20sf for Tan Brown. I did the install myself, but didn't have any sink cutouts. Lots of installers are now buying the prefab stuff, instead of slabs, and somehow the consumer is often still paying close to $100sf. You need to find a prefab outlet and see if they have an installer to recommend. The place I bought from is the Granite Outlet in Rancho Cordova (near Sacramento)
Granite Outlet, Inc. perhaps they have contacts in SoCal. Everyone of the budget places (we have at least 4 in the area) are Chinese owned businesses, so I'd assume that they have the contacts in China to get to the granite source. At the place I bought from they have frequent deliveries of shipping containers full of slabs. They come in counters with just front bullnoses and right or left ends bullnosed, in 8, 9 and 10 foot lengths. Peninsula islands are 36, 39 (and sometimes even wider) by 8 foot or longer.
Just keep checking to find a budget place. From what I've seen they don't do a good job of advertising. If these places are in Sacramento you have plenty in SoCal.