You pay CA sales tax even if you buy a car out of state unless you keep the car out of CA for a certain period of time (maybe 6 months???) before bringing it in and registering it.
I got my 19 platinum white Fiesta ST w/ black wheel for $18,421 earlier this month after contacting about 10 dealers in SoCal area. Without the platinum white color option ($595), it would have been $17,826, which is very close to your $17,750 offer. There is always a chance that you may get a better deal, but the offer you get is pretty good, or it was good enough for me.
I considered buying an out of state car, but when factoring in the airfare, gas, and other costs as well as time and hustle, it didn't make much sense. No one was giving enough extra discounts to compensate for them.