Online car rental broker Rentalcars.com, a British company, quotes the lowest prices online because they are not upfront about the additional fees you'll have to pay on the back end. The "Total Price" quoted online, the "Total Price" listed on your booking confirmation, and the "Total Price" receipt that they email you are all the same amount, but that price is nonsense. It's absolutely not the "Total Price" you'll end up paying and there's not a word about additional charges, which would at least give you a heads-up. In my case the "Total Price" quoted online and emailed to me twice by Rentalcars.com for a car from EuropCar Heathrow London was $159.78. The actual final cost was $362.47, which is an ADDITIONAL 144%!
Today, the extremely rude Rentalcars.com "customer service" rep, who constantly cut me off in the middle of my sentences, finally admitted that the "Total Price" listed in those three places is the "total price payable to rentalcars.com, and doesn't include additional charges payable directly to the rental car company", and that I should have taken the opportunity to read more (the fine print) by clicking on 'Manage My Booking'. Due to strong US laws, Americans generally trust that when a seller tells you this is the "Total Price", that means what it says. By not revealing the dirty secret in the actual documents they send you they are, by US Consumer laws at least, dishonest and they could be prosecuted for such. Unfortunately for Americans, they're untouchable in the UK courts unless you want to spend a lot of money.