Airport Parking

I'm flying American to DFW on Friday morning, leaving at around 6:40, and then returning Friday evening, arriving back in GDL at 9:40.
I was thinking of just leaving my vehicle in the garage or on the lot instead of my wife having to drive it in the dark both ways. I would appreciate it if someone could give me an idea of what the parking fee would be for approximately 17 hours. When I was out there last Saturday, I asked one of the guys outside and he said 300 pesos for the day. Any info would be kindly appreciated. I would rather not park in the lot outside the airport.

300 is about right for the indoor garage. When you enter the parking area you can choose between 3 daily rates, the cheapest is about $120/day.

Isn't the only access to the parking area to the left and then take the ticket or is there another parking entrance where you don't park in the garage or the open spaces just outside of the enclosed garage?

To park in the long term enter the parking garage as normal and follow the signs to go up. As you get to the top level (the cheapest at about 110 pesos a day) you have to put the ticket you received when you entered into another machine that spits out the ticket you need to enter the third floor. It is very easy and convenient.