when you have to relax overnight and go back to the airport , is very inexpensive and close to the Barajas airport

Stayed at the Ibis Aeropuerto in Barajas in January 2012.
The hotel is very basic (as you would expect), but does its job for a sleepover.
The Barajas metro station is a good kilometer or so away along the road past a fountain opposite the hotel. Reception staff claimed it was 500 meters away, but, having walked definitely more than 500 we finally came across a sign “300 m to the metro”. Not exactly doable with bags, so their airport shuttle (quick and timely) was very helpful. The center of Madrid is about 1.5 hrs (and 2 transfers) from Barajas on the metro, get ready to climb lots of stairs (tip, some transfer stations, like Nuevos Ministerios, actually have lifts, which saves a lot of time and energy).
The neighborhood itself appeared quite grim at first sight, didn’t feel too comfortable walking back from the metro station at night. There might be a bus from the metro to the hotel, but I was not aware of it.
On the positive side, there’s a supermarket in the same building, to the left of the hotel’s entrance (if facing the hotel).
The triple room we had for two was so tiny we could hardly fit two big bags. I can’t possibly see three people fit in it. The room was poorly designed: you had to be left-handed to at least partially open and close the window, the coat rack was placed by the bedside in the far left corner of the room, so you had to walk the room fully dressed. Bathroom size was generous in proportion to the room size, however.
Breakfast was mostly edible, though the soft cheese, which was good on the first day turned sour on the second, presumably, having sat in the warm room for too long as they serve from 4.30 am to noon.
Wi-fi at EUR 5 per day is a rip-off in my view. There was a desktop computer, however, I am not sure how much it cost to use, if anything.
Overall, I might consider this hotel for a solo trip but the rooms are definitely too small for two people with big bags.

No free transfer after 23:00 as promised, the only way to get to the hotel later is taxi which cost 20 euro. No free WiFi. Far from metro. The worst thing is the staf! Very rude and their favorite frase: I can't help you. I think there are a lot of better hotels near the airport with better service.

This is a good hotel to stay before a flight. It has an airport shuttle, it is a 10 min. walk from the metro, the rooms are basic, but modern, clean and comfortable, and the rates are good. It was very hard to find by car, though. Make sure you check your map really well, or use your GPS, as it is not visible from the freeway or any major street. There is a car-park behind the hotel, or you can park on the streets around it, but you'll probably have to drive around for a while, though, before you find a space. There are supposed to be a couple of spaces in front of the hotel for momentary guest parking, but they were permanently occupied while we were there, and the front desk clerks did absolutely nothing to remove these cars, eventhough we brought it to their attention.
Overall, the front desk staff was less than friendly, bordering on rude. I sat in the lobby for a while, waiting for my husband to find a parking spot, so I witnessed the staff's interaction with several guests and they were less than willing to go out of their way to help anyone. We traveled around Spain for two weeks and sadly, Madrid was the only place where we encountered this less-than-friendly service.
I would stay here again only for the convenience of the location and moderate rates.