It pays to check what is included when comparing budget airfares, writes Jane E. Fraser.

Whether it's to save money or have more in the holiday kitty, leisure travellers are eternally hungry for discounted airfares and there are now plenty of carriers willing to feed them.

AirAsiaX this month joins Jetstar, Virgin Blue and Tiger Airways in offering cheap fares to Australian travellers.

They are able to do so because they operate on a low-cost model, eschewing the frills of air travel in order to keep overheads low. But what do passengers actually end up paying for their flight after they have bought a few comforts - or necessities - along the way?

On some low-cost carriers, it is simply a case of having to purchase meals and drinks as you go, while on others, you pay for absolutely everything, including checking in your luggage.

One of the low-cost airlines, Tiger Airways, prevents you from taking your own food and drinks with you.

The Sun-Herald compared the prices and inclusions of low-cost carriers to determine their real value.

We began by searching one-way flights from Sydney to Melbourne on a given day. Jetstar was the cheapest, at $79, while Virgin Blue's fares started at $115 and Qantas's cheapest seat was $127.

On a one-hour flight, Qantas would serve a free snack and drink, so we added $5.50 (cheese and crackers and a coffee) to the Virgin Blue and Jetstar fares. Given that it was an hour-long flight and Virgin Blue and Jetstar have inflight magazines, we did not add any cost for inflight entertainment.

However, as Jetstar flies to Avalon Airport in Melbourne, rather than Tullamarine, we added the difference in the cost of a taxi fare, which is about $40 from Tullamarine and $80 from Avalon.

After making these adjustments, the cost of the three journeys came within $7 of each other: $124.50 for Jetstar, $120.50 for Virgin Blue and $127 for Qantas.

For the sake of a few dollars, most travellers would be better off making a decision based on timetables and convenience, rather than price (unless they wanted to take a snack with them and find a cheaper way of getting into the city).

They might also want to take into account that they could earn frequent flyer points on the Qantas and Virgin Blue flights.

On international flights, it appears the difference between low-cost and mainstream carriers is more marked.

We searched for a one-way flight from Sydney to Kuala Lumpur and found a Jetstar fare for $418.12, including taxes. We added to this a $30 pre-purchased food and drinks package, a $7 comfort pack (blanket, pillow, eyeshade, toothbrush, socks) and $10 for the use of a personal DVD player for the flight, which came to a total of $465.12.

The cheapest available flight from a full-service airline was $659.77, which made the Jetstar flight a considerable $194.65 cheaper.

Malaysian low-cost airline AirAsiaX, which is now flying to Australia four times a week, is so far flying only to the Gold Coast but early indicators are that it intends to be at the bottom of the price range.

A one-way flight from the Gold Coast to Kuala Lumpur was listed at $250, then we added two meals at $7 each and a comfort kit for a further $7 (no inflight entertainment was available for purchase).

The potential catch with AirAsiaX is that it charges passengers to check in luggage, and while the price for a small bag is quite reasonable, a heavy suitcase can blow the budget.

The carrier charges $7 for up to 15 kilograms, then it jumps to $42 for up to 20 kilograms.

If you checked in 21 kilograms - not an uncommon weight for international travellers - you would be slugged $77.

This would take the total cost of the journey to $348, still the cheapest option but a big jump from the $250 you thought you would be paying.

THE EXCESS BAGGAGE STING

Cheap flights can become horribly expensive if your holiday shopping throws you into the excess baggage realm.

Many low-cost carriers now charge for all checked-in luggage, while all have considerable excess baggage charges.

In Britain, low-cost carriers such as EasyJet and Ryanair charge £2-£12 ($4.45-$26.70) for each checked-in bag, with a total maximum of 15 or 20 kilograms, depending on the airline.

Beyond this, you can expect to be charged about $13 a kilo, which could make a 25 kilogram suitcase cost you as much as $145 to check in.