SINGAPORE - When flying on a low-cost airline, one expects to fork out a little extra for creature comforts like food and drinks.

But which items sold on board offer bang for your buck, while which are seriously overpriced? A price comparison by travel site Kayak.sg aims to tell travellers which budget airlines mark up which items.

Of four airlines that fly to and from Singapore - Tigerair, Jetstar Asia, Scoot and AirAsia - AirAsia was found to have the lowest prices for their snacks and drinks overall.

The prices are based on inflight menus on the airlines' websites as of May 16, Kayak said.

For example, a tea or coffee costs $1.70 on AirAsia but $4 on the three other airlines. Cup noodles cost $5 on the three airlines and $2 on AirAsia.

Compared to supermarket prices, however, prices in the air are nine times more, on average.

Budget airlines charge between $2 and $4 for a bottle of mineral water, which is more than five times more what a supermarket or charges, Kayak said.

Crisps cost between $2 and $4, about three times more than at a supermarket.

Tea is the worst-value item fliers can get, according to Kayak, as a sachet of tea costs only about six cents at the supermarket.

At $1.70 a cup, it costs 28 times more, and at $4, it is 66 times more than the supermarket price.

Said Ms Debby Soo, vice-president of Kayak Asia Pacific: "Low-cost carriers are providing a service when it comes to food and drink on board, which accounts for some of the mark-ups we see.

"However, it pays off to plan ahead and eat before you board, especially for short flights."