I just got back from Hermoupolis, the capital of the island of Siros, and I found rooms that I think were a cut above the rest on offer. Siros, by the way, is worth a couple of days: it's a beautiful city, all built in the mid-19th century, with elegant marble streets and sidewalks.
The most important thing about these rooms is that they are quiet! The place is on a little stairway street, without cars. Rooms have cooking facilities. The lady who runs it is delightful and very hospitable.
My room had a great balcony and was very reasonable at 30 Euro a night for one person (in May 2012). She also has rooms with more than one bed, in case you are traveling with children, etc. There is also a great roof deck if you follow your nose up the stairs. The place is about five minutes' walk from the ferry (directions below).
It's called Rooms Hermoupolis. Phone (22810) 87475; mobile (6937) 135880 or (6932) 736891. Web site is www.hermoupolis-rooms.gr.
DIRECTIONS: As you get off the ferry, you're facing the harbor street. Go to the right about three minutes. You'll see a little alley going to the left called Naxou. As of May 2012 there is Bank Geniki on the corner. Go up the alley, which has stairs. Follow it up across two small streets and you'll see the sign. (Naxou is now called Kosma, but it's a straight shot.) In case she is full, there is another room place around the corner, with a sign.