Any car at this age is a stepping stone. Id avoid spending under £1000. I'm on my fourth car, (I'm 22), but my fourth, a 51 plate ford focus has been a faultless runner so far (over a year). It costs me £1750 with 50,000 miles on the clock, and air conditioning and alloys, amongst other extras.
Dont forget that its almost guaranteed that you'll damage your car in some way. I know lots of people with 06-09 plate cars who have damaged them and significantly reduced their value.
If you want to spend that much, be prepared for it to be a poor investment and ultimately for you to lose a substantial amount of the money you paid for it.