This week, I set out to find the cheapest possible hire car for a week in Spain. As all the companies below will point out, a simple price comparison will always be misleading - not just because drivers will be offered additional insurance cover when they collect the car, but also because these basic quotes may exclude excess-charge waivers, theft protection, fuel, airport surcharges and all kinds of baby, luggage and ski-related extras. Several impose different conditions on inexperienced or accident-prone drivers. They all, however, represent the cheapest car available for the same week in April, collected from and returned to Barcelona airport at noon.

travelocity.co.uk £103

Travelocity and Opodo search various rental companies for the best rates, and returned almost identical prices. Travelocity beat its rival because the latter was unable to show the terms and conditions of the deal - a technical problem its lawyers need to rectify as soon as possible - and also because Travelocity showed exactly how much the excess charges for tax, airport surcharges, the collision damage waiver, theft protection and personal accident insurance would be. (At this price, the VAT alone would add £16.50 to the cost.)

opodo.co.uk £103

Opodo is a slick operation, but it does have one additional drawback: it only allows you to pick up your car from and return it to an airport.

holidayautos.co.uk £104

The "trusted partner" of Expedia and OTC, Holiday Autos has a solid and reliable site. Note that the price is £5 higher if you book offline.

thrifty.co.uk £117

Thrifty's hire includes many of the extras that other companies leave out of their basic price, but why are some of the extras still being quoted in pesetas?

hertz.co.uk £117

Hertz quoted a cheaper rate on Opodo than it did on its own site. But the vehicle guide, which shows you exactly which cars are available from every Hertz outlet, is rather good.

avis.co.uk £126

Well-designed and executed, Avis also stands out for the fact that it allows customers to change or cancel an existing reservation online.

budget.co.uk £132

Like Thrifty, Budget's quote represents better value than some of its competitors, but the site is a little unwieldy.

e-sixt.co.uk £183

With only a top of the range Toyota Corolla available on a date two months in advance, e-Sixt was an unimpressive performer particularly since it also offered the cheapest rental of them all via Travelocity. To add to the confusion, the site has no currency converter to change euros into pounds.

NB Readers hiring a car in the US should also try the North American specialists alamo.com and dollar.co.uk, neither of which operate at Barcelona airport. The latter also suggests a number of excellent four- to six-day itineraries in Oregon, Hawaii, Pennsylvania, San Francisco, Florida, Alaska, Wyoming and South Dakota.

Email: ros.taylor@theguardian.com