cook islands accomodation

I'll be arriving in the Cook Islands in late November, staying till mid-December.
I'm on a fairly tight budget, but hope to explore some of the outer islands. My question is--since it looks like there aren't many hostels in the Cooks (and no camping), do places tend to fill up? Should I book everything ahead, or can I get by with just booking a place for the first night or so, and taking things as they come for the remainder of my stay?
Also, any favorite-experience tips would be appreciated!

I started a thread on the Cooks last month that contains some hotel recommendations, but I am on a higher budget: http://www.lonelyplanet.com/thorntree/thread.jspa?threadID=2351552. This does not appear to be a cheap hut on the beach type of travel destination (which is too bad--I enjoyed a good fale stay in Samoa :) ). I bought the LP chapter on the Cooks, and low-end accommodation seems to start at $50 on Raro, slightly less on the outer islands.