The Skyline lover in me wants to tell you to go ahead and do it... the Mum, investor, business person in me has to tell you what I have always said "if you want to get ahead, the best investment (in a car) is driving the cheapest car your ego will allow".
You mentioned you would have the 18k in cash, consider investing it and using it for an investment property down the track (while still staying at home) on an interest only loan (rent pays the interest) then by the time your ready for interest + principle your investment will be worth a hell of a lot more than your loan is.
If you're talking about taking out a loan for the car... I'd suggest waiting a little while longer, get something you can park at uni without living in fear every day of whether its safe or not. If you do get the car (any car) ask your insurer if they will give you fire, theft and 3rd party rather than just 3rd party.
I bought a property last year which is today worth 20% more (in less than 12 months), that equity alone could be used to finance a car plus the deposit on the next investment property (get my drift?).
But I'll support your decision either way, after all, I did say "what your ego would allow"