Here's the definitive answer as i asked the parking attendant this evening.
Tariff is 245 pesos for the first 24hrs and 175 a day thereafter. Park in the lot up the hill, opposite the terminal, above the coach park. Make sure you let the security guard know how long you intend to stay and he will register your vehicle in the system. The lot is patrolled by security personnel and there are CCTV cameras in operation.
Abandoned vehicles are towed after a period of time. Surprisingly, quite a few vehicles are abandoned at airports. Those that can't afford the payments and skip the country and stolen vehicles.