Have in mind, that since I am 23 now, and this is my first car in the UK, the prices I am going to pay are a bit high (I think).
For the cars mentioned above for full comprehensive I can get around £700-800
a year if paid once off.
2003 350z - 5.5k is doable - 6k better.
Insurance £800 ish @ 23/24

Terrible fuel economy, lots of fun.