You're going to be more expensive no matter what since you're in California. That said, try skipping the landscape yards/rock outlets and just figure out which local quarries those places are getting their material from. It'll be just one type of rock, but it'll be cheap because it's local. Bonus points, it'll look like it belongs in your backyard instead of some exotic boulder from Montana.
Around here, it's basalt. I can get it across town from a yard the quarry owns for less than $80 ton. Any size from 8" up to 6' across. I can also get the exact same rocks at 5 other places close by for anywhere from $125 to $200 ton.
Get the phone # to the scale or onsite office at the local quarry. Call 'em up and ask if they're open to the public. If not, ask if they know any drivers who do residential deliveries from their quarry. Get those phone #s. Call those folks up and order from one of them.