first thing you do when buyin a car (or should) is see if you can afford the running costs.
Insurance is a running cost, so if you cant pay it, sell the car and get something you can afford to run.
Just to put it in perspective ive spent over the last 5 years on my car insurance = £6000 + car at £1,200 + 2lt conv £3500 total = £10,700
That doesnt include petrol,road tax, servicing or tyres. As a student it has cost me more than 60% of my money to run a car.
So if you cant afford the £900, sell the car and get something cheaper or GIVE UP OTHER THINGS to compensate.