I've been able to reduce the 1-week rental cost for a Budget car in Kona for 3/12 -19 from $276.18 to $183.77, by using the BCD U109001. This is a NWA WorldPerks discount offering 40% off Budget rates. Just for good measure, I've also joined the NWA WorldPerks program and have an official number. The actual percentage reduction may be somewhat less, as some of the fees associated with the rental are fixed, rather than based on the rate.