WillowAzore: my first car was a Rover 100. Its engine was a 1.1, it cost £300, the insurance was £550 for the year (I was 22) and she lasted me 6 months! Total rustbucket, but I adored her.
My second car is a slight upgrade: a '96 Fiesta. A far better car but not in my heart like my first was!
All the advice here is bang-on: don't bother with anything very expensive or flashy-it costs more to insure and like me, you're bound to have a couple of knocks and dents!
Get something reliable and sturdy with a reasonable service history-ask sellers to tell you about work they've done/had done on the car, and previous owners' work too.
No funny noises when you go for a run before buying, no clouds of black smoke from the exhaust. Beware of sellers talking rubbish about it being used once a week for shopping.
My first car, the Rover, was advertised on Ebay, and also on a car forum for little boy racers (where it was advertised as "slammed", or lowered). Watch out for that too as you may get very different stories depending on the sellers' audience.
Let us know what you get, first cars are amazing! x