Amsterdam is one of those places that is such a popular tourist destination that, half the time, you find that prices are dearer at weekends than during the week.

A good place to start for an idea of prices is http://www.bookings.nl/

I don't find Amsterdam hotels particularly wonderful: they are behind many other countries in terms of amenities (and often décor). But, they're usually efficient, cheerful little places. Do bear in mind the Dutch sense of humour can be very scathing, and what many may take as an insult is little more than humour (I've seen several USAians offended in this way...)

There's more than one 'city centre' district: you have the canal belt (centred around de Dam), with clusters of hotels around Nieuwezijds Voorburgwal and de Dam itself. Then, you have Rembrandtplein and Leidseplein: gaudy, neon-strewn bar districts. Further out (but close to several attractions, and still a short tram ride from the canal belt) is the museum quarter.

Finding accommodation at a reasonable price is often a lottery. A good alternative is an apartment - I recommend the de Monnik apartments (http://www.de-monnik.nl/) who do not always enforce a minimum stay.

Otherwise, I'd go for Priceline, as the prices are so variable.