I seem to remember that at the Las Vegas airport (LAS), if you took the rental car company's shuttle bus to the rental car lot, you were subject to the airport fees, but not if you got there on your own. I think I once ended up taking a taxi for the very short trip, it ended up being cheaper than what the fee would have been.

However, this was when each agency had their own lots in various places around the airport terminal, prior to the opening of the consolidated rental car facility, so don't know if that's still the case any more.