When I was in Sixth Grade, I went with six friends collecting for our school. We were going to go in a Limo, which we managed to arrange for the same price as a taxi (The taxis charge per hour, and we found a Limo for the whole night) – it wouldn’t have cost us a penny more. However, we were advised against it by other groups who have taken limos in the past and found that they were received less warmly than in years that they took taxis.
BTW – There is a big difference between a collected from Israel paying airfare and hotel – if the collector told you he had a first class ticket and was staying in a five star hotel, of course you wouldn’t give him a penny. If a limousine is more expensive (which it is in most cases), then obviously using tzeddaka money is not ideal.