Since there are only 3 bridges that span the Grand Canal, sometimes you'll find yourself stuck on the wrong side of the canal. Instead of walking all the way to the next bridge, you might just jump on a traghetto. The traghetto will take you from one bank of the canal to the other for less than a Euro. It's also a great alternative to the gondolas, which are very expensive.
If you want to feel the emotion of having a gondola trip for less money, you can go to one of the seven 'traghetti' (ferries) working in Venice: you will be carried from one side of The Grand Canal to the other: the 'traghetti' are often used by the Venetians.