Betsy Malloy, our guide to California Travel, just returned from Carnevale in Venice. She stayed at a convent, Istituto San Giuseppe, about five minutes from Saint Mark's Square, for 37 euro per person without breakfast (note that many hotels charge high season prices during Carnevale). She says, "it was clean and had a nice bathroom with a shower. Very secure because you have to buzz in and out so it's an especially good choice for women traveling alone."
Betsy also recommends Alla Corte Rossa (book direct), an inexpensive hotel close to the parking terminal. Bed and Breakfast inns can be budget choices, too - see Bed and Breakfast in Venice.
Good info. I’m glad the convent checks out as I was planning to use it on my next trip to Venice later this year. I found it on http://www.monasterystays.com which has a booking service for lots of monasteries and convents all over Italy. Your readers might want to check it out as it can save a lot of time especially if you don’t speak Italian like me
John, it would be helpful if you would link to the monastery we’re talking about. I think this is your link to the Venice monastery. Although it costs more, the cost covers making the reservation, which is usually more difficult than making a hotel reservation.