I tried round about 20 (personal) messages on couchsurfing already without any success so far... - my budget this month is quite tight, cause i'm heading to Cyprus next month.
I was trying to find cheap options too... but Amsterdam is sooo expensive. Just one bed in mixed room is 30-40€/day lol.
Finally I took "The Student Hotel", but it is about 100€/night... and is one of the cheapest one.
I guess your plan is going to be impossible, unless you find some friend or you sleep on the street.
Problem solved - Amsterdam, here I go!
Thanks everyone for your hints & tips - and see you in Amsterdam