Avis - First time renter...

So I am heading off to Orlando in April for 15 days and I have been looking at rental cars for a few weeks now and this Avis deal seems to be the cheapest...

Base rates:
Standard/Full Size: $522.14
Premium: $475.73

That seems like a pretty good deal, especially the premium, my question is, what I am likely to receive at the airport if I choose the cheaper Premium rate?, being from New Zealand I have no clue about the models, I am staying about an hour out of Orlando and would prefer not to get a Crown Victoria or anything that looks like a New York taxi or a V8, but if thats all they have is it possible to ask for smaller car? or would I lose my above rate?

Its pretty daunting to be honest, never been to the USA and here I have only rented a car once from a very small local rental car company who we know well, so not really sure what I should be looking out for or what I might end up with, I dont mind a big car at all and would prefer it over a small car, but I would prefer to get nothing bigger than a V6, reason I chose Avis was its one of the best places to rent here in NZ and also I want one whos at the Airport onsite, also I am 23 so I understand the Premium is the maximum car class I cant rent( I have spoken to Avis and I am aware of the $27 fee per day =-(

Any help or advice would be much appreciated at this point, Thanks!

Orlando is a really big Avis location. They have a big fleet, although it can be depleted at busy times. If you reserve Premium, get assigned a Mercury Grand Marquis but want something smaller, just ask for it. U.S. rental agencies buy lots of different vehicles and make ample use of the 'or similar' wording such that there can be lots of vehicle variation even within a reserved class. Enjoy your visit. (Current U.S. fuel prices are generally a bit less than USD 1.00 per liter.)

Thanks for the reply, much appreciated! =-)

Why don't you simply rent an intermediate sized car. It will be what you're looking for, and it will save you money.