1997 Nissan Altima Car Wont Start, Mechanic trouble

I was driving my car back from El Paso to Austin when I stopped to get gas. I turned off the car, got out, and realized I was too far from the pump. I got back in moved the car 3 feet, and pumped gas.

When I was done pumping gas, I got in the car, turned the key, and nothing happened. the dashboard lights and radio all turned on, but the engine wouldn't turn, not even a click from under the hood.

I tried changing it into neutral, jiggling the gear stick in park, checked fuses, got a jump from another car... nothing.

finally I had it towed to a mechanic across the street from my job.

The mechanic says the following:

The cables, battery, and starter need to be completely replaced.

He can completely replace the battery cables for $400, (later, he called back to say $700 because I need a 'wiring harness')

He can replace just the terminals and battery for $389.
he can replace the starter for $400.

It seems to me like I am getting taken for a ride, but since I know NOTHING about cars, I have no way of confirming this.

Does any of this make sense? Would replacing the wiring harness fix the problem? how badly is he trying to rip me off?

Any input would be valuable.

Thanks,
Ricky