When booking a holiday you have the option to book the accommodation and the flights yourself or as part of a package. When booking your flights you may find quite a drastic change in the prices from company to company. It is always worth looking at flying from different airports as sometimes you will get a much better deal from one to the other. The other thing to check is the date you are flying as again you can often save even hundreds of pounds by flying a day or two either side of your original selected date.
Many people use flight comparison sites to check which company is offering the cheapest flights but they may not always give you all the information upfront and you will often need to look in to exactly what is included in the price.
Often there is no baggage allowance included in the cheapest flights apart from cabin baggage. With additional suitcases costing on average £25 per 15kg each way, this can very quickly add £100 or so on to your holiday price. You should also check to see if transfers to and from the airport are included as again this can push the price up.