Previously we have taken a cheap one from Aldi or Lidl or somewhere like that, took it over in the empty suitcase that was to be filled with clothes purchased in the USA, used the cheap booster seat for the duration then threw it away after we'd off-hired the car. Total cost £3.99 if I remember correctly. This was for a child that just needed the height boost for the seatbelt to fit correctly, but I've seen seats at Toys R Us suitable for younger children at around the twenty five quid mark that I would still deem to be disposable compared to the cost of hiring one.