Amsterdam was probably the most expensive European city I went to, but it is doable on a budget. We stayed at the Flying Pig Hostel, I can't remember if it was uptown or downtown but it was the one near the train station. It was alright but not one of my favourite hostels, and pretty expensive at £30 a night for a 16 bed room, although I didn't find anywhere with good ratings cheaper.
If I were to go again I'd definitely take more money and more people. Anne Franks museum is a must and we went to both the sex museums, they're much of a muchness but quite funny, don't bother with the torture museum, not very intersting. We were lucky when we went as there was a free festival called Uitmarkt for the three days we were there. It was spread out over about 40 venues, indoor and outdoor, and had all kind of music and dance.. I'd probably say that was the highlight of my time in Amsterdam, that or getting a tour of the red light district by a scottish stag party. So if you're going to go I'd recommend going at the end of August when that festivals on.
You also need to account for more money if you want any weed. I think a space cake costs about 6 euros, and drinks are ridiculously expensive. About 5-6 euros for a vodka and sprite. And I think 3-4 euros for a pint.