Cheapest possible bed in Amsterdam next to sleeping outdoors?

hostels or couchsurf

What time of year? That is a huge factor for hotel costs in Amsterdam. Amsterdam for lodging is a very expensive city. Staying out of the city would be cheaper.

The tickets are for October 10-21 only.

Go to booking.com and sites like that for Amsterdam and Haarlem. Haarlem will be cheaper and is a short bus ride or train ride into Amsterdam!

Try campsite Zeeburg Amsterdam, all year open, they have single person ecocabins for around €35 a night, tram stop nearby. Or bring your own tent with you will be cheaper, pitch around €10 a night, think you can hire a tent too. https://www.campingzeeburg.nl/en/

Just outside Amsterdam is campsite “ ‘t Uilenstekkie” , tent pitches starting from €6 a night, busstop nearby. No idea all year open. http://www.uilenstekkie.nl/?lang=uk

These are excellent ideas. Wil, thank you so much for the information about the eco campsites. I had no idea they existed! You have been very helpful. I will pass this information on immediately.

Great information :)

If your friend is a people-person, then definitely look into Couchsurfing.org. More than just free accommodation, it's an opportunity to connect with people who give great local travel advice and often act as tour guide when they have the time. It can sometimes be difficult for a new couchsurfer to find hosts so your friend should join soon, meet some others in the network and gather some references.

I just plugged in those dates on Airbnb, selected "private room" and "shared room", slid the price meter down to $50 or less, and got almost 40 places between $15 - $50 per night. I've used private rooms on Airbnb before and had excellent experiences staying with local people in many countries. Worth looking into!