Frugal passengers determined to save money may want to pack their own lunchboxes, especially if they've booked with Ryanair.

A meal onboard the no-frills Irish airline can cost more than the airfare, a new study by travelsupermarket.com shows.

The survey found that some budget airlines marked up their food and drink as much as 10 times the price at supermarkets. Still water on Aer Lingus was marked up 1,083 percent.

But Ryanair was the worst overall offender. The Dublin-based airline is famed for its innovative approach to making a profit - see their 5 money-saving schemes that would impress Scrooge.

When passengers are held hostage 37,000 feet aloft aboard Ryanair, they are charged 2.76 pounds (US$4.36) for a half-liter bottle of still water.

Add a cup of tea, a cup of coffee, a sandwich, a small tin of Pringles, and a snack of Walker's shortbread, and the bill comes to 18.07 pounds.

That's higher than the 18 pounds flights Ryanair is currently operating from Liverpool to various European destinations, including Barcelona and Warsaw.

It's enlightening for anyone -- and that's everyone -- who has ever wondered how budget airlines can offer such low airfares and still make a profit.

Other than food and drink mark-ups, other hidden charges can crop up if passengers do not read the fine print.

This month, 35-year-old British housewife Suzy McLeod was charged 236 pounds because she forgot to print her family's boarding passes before arriving at the airport.

Despite this, Ryanair continues to do good business.

In July 2012, 8.72 million passengers bought seats on Ryanair flights compared to 8.08 million during the same month last year, according to figures released by the company.