You know we can't determine the cost because we don't know what's damaged and what you will insist be fixed and what you're willing to overlook. Start by flooding the interior with fresh water from a garden hose to wash the salt out. At this point more water isn't going to hurt anything that isn't already damaged. Use a wet / dry vacuum to remove the water, then use a fan to dry the interior. Home Depot has real nice ones made by Ridgid. If the battery is dead, do not recharge it yet and do not replace it. Be sure all the electronics are thoroughly dried before attempting to apply power or turn on the ignition switch. The many computer modules under the hood are sealed from rain and should be okay. There's also many computers inside including the radio which are not sealed. Those are the ones to be sure they're dry.
You'll also want to flush the unibody frame rails to wash out as mush salt as possible. Check the engine oil and transmission fluid. If they're normal, no water got in. Those should be sealed pretty well. If either is overfill, drain and refill them before trying to start the engine. The transmission can be hard to tell because it will read high when the engine is not running. Recheck it once the engine is running, then if it's overfull, have it flushed and refilled. If the water got high enough to get into the air filter, it may have also gotten into the cylinders. Remove all of the spark plugs, then bypass the starter relay or solenoid to crank the engine without turning on the ignition switch. If water is in the cylinders that will blow it out and prevent hydro-lock.
The biggest concern with import vehicles is the wiring harnesses. When water wicks into the wire strands it will cause corrosion that you can't stop except by replacing the entire harness. You could be chasing intermittent electrical problems for the rest of the life of the vehicle. New harnesses from the dealer are unreasonably expensive. Instead, find an identical vehicle in the salvage yard and remove those harnesses if necessary. If the water didn't get high enough to submerge the wiring you may not have any related problems in the future.