We are constantly told that if something seems too good to be true then it probably is. Instinctively we look for a catch. But as prices drop lower and small print gets longer, it could pay to do your homework before jumping on a no-frills flight. Before you book, look closely for hidden costs which could easily bump up the price of your trip. Low-cost airlines may only offer flights from less busy airports such as Luton or Stansted. Depending on where you live, this may involve additional travel time and cost.

From central London you need to factor the following costs and time into your plan:

•  Gatwick Express from Victoria Station takes 30 minutes and costs £24 return.

•  Heathrow Express from Paddington takes 15 minutes and costs £26 return.

•  Stansted Express from Liverpool Street takes 45 minutes and costs £24 return.

•  Thameslink from Kings Cross to Luton takes 35 minutes and costs around £22 return.

Get what you pay for

When you board a low-cost flight, expect to be crushed in the mad rampage for the best seats - all of which are unallocated. In terms of drinks, meals and entertainment, prepare in the same way that would for a bus or train journey. In other words expect nothing, take your own scoff and magazines plus plenty of cash if you fancy a gin and tonic when the trolley comes round. A no-frills flight does exactly what it says on the tin so if you have not been on one before, you could be in for a culture shock.

Tighter schedules can sometimes lead to reliability problems and you certainly wont be pampered on board. If you forget your packed lunch expect to pay around £4 for a sandwich on a Ryan Air flight plus about £2.50 for a beer and £1.50 for tea or coffee. MyTravelLite sandwiches are about £3, a glass of wine £2 and tea or coffee £1.50 a cup. EasyJet does snack packs with cheese, crackers and pate for around £2.50. Soft drinks or beer are £2 and tea and coffee £1.50.

UK to Rome

So what can you expect to pay for your flights and does it make a difference if you depart from a quieter airport? If you are heading from London to Rome in mid-summer for five nights then easyJet charges £139.98 for a return flight. Ryan Air comes in cheaper still at £116.80 and the price is the same from Gatwick or Luton so there is no pressure to roam further for a lower fare. British Airways flights cost a total of £218.50 which includes a hefty £45.50 in taxes and surcharges. If you fly from Birmingham, the price drops slightly to £187.50 but this is not such a saving unless you live locally. Otherwise expect a one and a half hour train journey from London at a cost of around £50 return plus taxi fares to the airport. National carrier Alitalia offers a cheaper deal from Heathrow of £186.10 including taxes. Travel from Newcastle airport and easyJet flights cost £114.98. BA will take you from Newcastle via Heathrow for £260.10.

UK to Malaga

Travel to Malaga and Birmingham-based MyTravelLite wants £158.59 for flights. But you can go from Gatwick with easyJet for about the same - £159.98. Incidentally, Gatwick came up as a cheaper option than either Stansted or Luton for this flight, proving that departures from the main airports are not always the most costly. British Airways can also fly you most cheaply from Gatwick but with taxes and surcharges of £37, their final fare is £208.00. Finally, Spain's national carrier Iberia offers the least impressive deal. Not only does it cost £216.40 return (£47.40 of which is taxes and charges) but it stops at Barcelona on the inbound flight. From Newcastle, easyjet flights cost £204.98 and BA charge £316.00, once again with a stop at Heathrow.

It may be dull but read the terms and conditions of the ticket before you buy. Most cheap flight tickets are non-refundable and non-transferable.

Here are 10 tips to make sure the price is right:

1. It goes without saying that you should shop around. Try several airline websites for reductions and special offers - particularly online discounts - which may rival or better the first offer you have seen.

2. If possible, aim for midweek flights as they will almost always cost less. There may also be cheaper options a day or two either side of your first choice date so it pays to be flexible. Flights on a Friday, Saturday and Sunday usually attract a weekend supplement. Avoid departing on these days if at all possible although with many airlines, including a Saturday night in your stay means you will be classified as a 'leisure traveller' and could benefit from a reduced rate.

3. Don't book at the last minute. Flight costs work differently from package holiday costs - the price usually increases as you get closer to the date of travel so the further ahead you book, the better the deal you are likely to get.

4. Make sure your travel insurance covers you if the carrier goes bust. Again, unlike package deals, flights contracts don't usually have any protection built in if the worst happens. The same applied to cancellation or delays where cheap airlines may offer no compensation - or even a free cup of tea - if you are stranded.

5. Double check that you are booking direct flights unless you are relaxed about stops.

6. Be clear about which airport you are flying into. Some cheap flights head to out of town airports which may be 50 miles or more from your city destination and mean spending more time and money to reach your hotel.

7. Because many airlines and flight agents now offer accommodation, it is worth searching for hotel and flight packages as the total cost could be much cheaper than booking flights and hotel separately.

8. Check the baggage allowance - it may be considerably lower than other airlines.

9. Be aware that no-frills airlines don't offer discounts for children, so they pay the same fares as adults.

10. 'Free' or '99p' flight deals may look tempting but they generally only apply to a tiny number of seats or flights. Hidden costs may include taxes, surcharges or the discovering that the offer is only one way and a return flight will cost an arm and a leg. Read the small print before you book.

Prices and other airline details correct as at 1 July 2005