Originally Posted by AutoSlash

All of the models you mentioned are from Hertz Collections. There is effectively zero chance you will get a free upgrade and will have to pay a significant per day upgrade fee if one of those is even available. It probably doesn't much matter what you book initially as I don't think that it's going to have a significant impact on what they quote as an upgrade fee to move to an entirely different class of vehicle. Probably just book whatever class:

a) Seems like the best value for the money

b) Whatever class you'd be happy with if no Collections vehicles are available.

You can try to call/email, but I'm guessing the local manager of a major airport localtion has more important things to worry about than trying to find you an upgrade for a 1-day rental. Yes, I know you are a PC member. So am I. And so are probably hundreds of other renters who will rent at IAH the day you are there.

All of that said, IAH is now a Hertz Ultimate Choice location. As a PC member, you can reserve an intermediate car or above and choose from anything in the PC section. While you will generally not find any BMW/Mercedes/Audis there, you may get lucky and find one in the Premium Upgrade Zone where you can upgrade for $25/day (plus taxes and fees) as a PC member. Keep in mind though that we're talking standard BMW/Mercedes/Audis not M/AMG/RS models. Those are almost certainly going to carry a heftier upgrade fee.