So I'm looking at buying a car. At the moment I am using my parents' old car, however when I move out of home I will not be able to take it with me, and it also lacks some of the features I would like (cruise control in particular).

I'm looking at buying a small car, probably a hatchback. At the moment I have saved around AU$12,000. My parents are willing to lend me some amount, probably up to $5000, and I work for a bank which can give me a loan at a very favourable staff rate. I earn a bit over $325 per week at the moment and I have few living expenses beyond luxuries, that income is bolstered semifrequently when I can work extra shifts. At the beginning of 2013 I will be seeking a full time job as a high school teacher.

Looking at a few car websites (in particular carsales.com.au) it appears I can buy a fairly good second hand car for around $15,000, or a brand new car that seems quite good for around $24,000. This is a very rough guide to local prices.

I am aware that my decision process in this judgement is very fallible because I don't know much about buying cars, e.g. the potential pitfalls of a second hand one, and any other things I need to take into account.

Being as this is by far the most money I will ever have spent on a single thing and it is likely to last me for most of a decade at least, I am strongly motivated to make this decision rationally.

Does anybody have any advice they can give on how I can decide how much money to spend, or things I should consider when comparing potential cars?