A family hiring a standard family car in Malaga for a week in June could hand over an additional £346 at the rental desk when picking their car up, when the original hire charge was just £173 for the week.

Purchasing excess car hire insurance (at £159), extra driver's cover (at £43), a child's car seat (at £63) and a Sat Nav (at £81) from the rental desk will push the overall cost up by an additional 100%.

iCarhireinsurance.com, the leading stand-alone provider of excess car hire insurance, has compared the prices of four rental companies at seven popular destinations for the June week of 10-17 June 2013 to reveal the hidden costs at the rental desk.

Looking at the destinations of Barcelona, Faro, Malaga, Milan, Nice, Tenerife and Corfu, iCarhireinsurance.com found great variations in the costs that travellers would be paying at each destination.

A Child's Car Seat - This could set you back up to £83 in Milan for instance. The average price was around £50 across the destinations, apart from Corfu and Tenerife where it was around the £30 mark.

An Extra Driver - Putting an extra driver on a policy can be costly ranging from up to £76 with Hertz in Barcelona, to £31 with Avis in Corfu, to £12 with Sixt in Tenerife. Budget for around £40 as this was the average cost although if the driver is under 25 expect a steep hike again with an average charge of around £100.

Sat Nav - Buying a map might seem worth it compared with paying an eye-watering £90 to hire a Sat Nav in Milan from Avis. This dropped to a more reasonable £56 in Faro with Budget, to the best value of £37 with Sixt in Corfu.

Car Hire Excess Insurance - If excess waiver insurance is not purchased by a hire car customer they could be liable for up to £1900 if the car gets damage or even stolen. Visitors to Barcelona, Malaga, Milan, Corfu and Tenerife could be looking at a week's excess insurance costing them around £150 if bought from the rental desk - this is over seven times the cost of an iCarhireinsurance.com policy at £21 for the week (at £2.99 a day).

The most reasonable place to purchase excess insurance was in Nice, where it cost £84 on average from the four rental companies, however this is still four times more than an ANNUAL policy from iCarhireinsurance.com. iCarhireinsurance policies are also more comprehensive and cover vulnerable parts of the vehicle which are frequently excluded from the car hire companies' policies.

"When a small chip to the windscreen can cost hundreds make sure you're properly protected from unwanted costs by buying excess insurance before you fly," said Ernesto Suarez, founder and CEO at iCarhireinsurance.com.

Disclaimer: All prices contained in this article were correct on the original date of publication. Prices may change over time, so for current prices, please get a quote.