Well I am afraid its all bad news,
insurance is impossible and dare i say it is because of younger drivers or lets say least experienced drivers. I am 24 and I got my 325i when i was 22,
I had been trying to get that model of car since i was 17!!
Now I have seen the change in the insurance industry, its just getting more expensive, a very good friend of mine is a insurance broker and he said to me the bottom line is that the companies have had enough of making losses.
plus world economy 911 war etc all jack things up.
Bad news is that formerly some vehicles had 25+ age restrictions on them ie you had to 25 or older to drive >> 325i is 25+ , the rules have gone one worse now the same car is 30+ with many companies!
The better news is that with lower power cars they'll be cheaper in all respects, plus you get good experience, remember a car with a insurance rating less than 10 is better. Plus you will build up no claims hopefully!!
Or if you really want get a 318i, get it on your mum/dads name otherwise you will need a mortgage to insure it. Plus shop around try the net etc but watch out, i have had bad experience with the net, where a company under sold a policy which eventually was cancelled!
Good luck!