Etap Hotel is definitely the cheapest option of a hotel very close to Schiphol Airport. It is 7 mins away from the airport, slightly longer in the morning and evening rush. There is a courtesy shuttle bus every 20 mins.
The rooms are very small, furnished with Ikea type furniture. There is a (narrow) double bed and one bunkbed above it. The shower cabin is tiny, and I mean tiny. Breakfast is not included but there is a breakfast bar in the hotel.
This hotel is next to Hotel Ibis Schiphol Airport. They share the same shuttle bus.