I bought a 1.3 MK6 Escort for £550 for my first car. It wasn't fast but it fulfilled all the requirements of a cheap first car. It was also a lot less to insure than a Fiesta. Best thing to do is not to get hung up on any particular make/model. Go out and have a look at anything, be it a Mondeo, 306, Micra etc. It's your first car and you have £500, you can't afford to be fussy.