The past decade has seen cheap airlines go from strength to strength; so if you're able to spend some time on the Internet, and are flexible with your departure times, then it's possible to find a flight for less than the price of a cappuccino in St Marks Square. Increased competition has also driven down the cost of scheduled flights, so it's worth looking in the back of the Sunday newspapers and seeing what deals the big carriers are offering.
Venice is served by two airports: Marco Polo and Treviso. Most flights touch down at Marco Polo which is just 10km north of the city centre in the suburb of Mestre. From Marco Polo there are a number of ways to get into Venice, but be warned; some of them can cost as much as your flight. If you're going for a 'once in a lifetime experience' you might want to consider splashing out € 80 on a private water-taxi (motoscafo), otherwise you can share the cost with other travelers as each boat holds up to six passengers (make sure you establish the price first). Regular four-wheeled taxis, catering for landlubbers, cost €25. If you're hoping to avoid bankruptcy during your stay in Venice, then the ATVO shuttle bus service to Piazzale Roma is the best bet (journey time: 20 minutes, cost: € 3).
Treviso is used by a number of budget airlines and charter companies (it's actually called San Giuseppe airport), and is roughly 35km north of Venice. ATVO runs a Eurobus service which is timed to coincide with all arrivals and departures. Coaches operate between the airport and Mestre, from where you'll have to continue on a vaporetto (journey time: 1 hour, cost: € 4.50). To make sure that you get a seat on the bus it's worth making an online booking in advance. Alternatively you can catch the local bus to Treviso station and then hop on a train.