I drive a 15-year-old Nissan Sunny which has 95,000 miles on the clock and is only worth about £250 and I currently pay just under £52 a month for myself, with my brother and parents as additional drivers - so about £610 a year. However, that £610 a year is pretty expensive considering the make and age of the car and my age (over 25) and the reason it's that high is because I don't have a clean licence. If my licence was clean, I would probably only be paying around £300 or so per year.
For me, reasonable car insurance is anything under £500 per year (preferably closer to £300 but I won't get it that cheap for a while yet), expensive is £500-£1,000 and extortionate is over £1,000 per year - however, my family have always bought older, second-hand cars that don't cost all that much to insure... and we also can't afford to pay all that much, so none of us have ever paid more than a few hundred pounds per year for insurance.
Insurance will also depend a lot on your driving history too... as an example, I bought a 1995/96 Nissan Micra in 2006 and it cost £465 a year for myself and my parents (I had a clean licence then, but was the most expensive driver). My parents bought the car from me in 2007 when I moved to the US and the insurance went down to £144 per year for the two of them (they had 5 years no claims and already held another policy with the same company for their other car, so got a discount). A few months later, after my youngest brother passed his driving test, he became the main driver and the insurance went up to about £800 per year for him and my parents (he's now the most expensive driver)... all for the same car.