Your options as a Gold member is to accept the vehicle you are assigned at LAS or look in the Gold section of the Ultimate Choice lot for a possibly superior choice (note - LAS may just direct you to the Gold section without assigning you a specific vehicle). If you try and take a vehicle from a section other than for Gold members (eg, Five Star, President's Circle, or Premium Upgrades) you will either be denied from exiting the lot or asked to pay an upgrade fee (which is variable and not fixed).