What's the real cost of my driving?

Today I've been trying to sort out my car insurance and see if becoming a member of the IAM will do much to put a dent in my premiums. I'm actually waiting for some information to come back to me, so while all my car details are out, I thought I'd take a few minutes to do something I've been curious about for a while: work out as accurately as I can just how much it's costing me to run this car.

Depreciation
My current car is a 2005 Ford Mondeo 2.0TDCi 115bhp and I've had it just over a year and a half (since 12th November 2009). I bought it for £4250 back then. Depreciation is hard to work out, so I looked for the closest matching car on AutoTrader and tweaked the numbers appropriately. By my reckoning the car is now worth £3300, which means a depreciation of £950 (22%).

Straightforward Costs
Car insurance so far has cost me £918.42 (a full term, and a partial term with an added premium to my insurance coming from the old Corsa), Car Tax £250 (2 x £125), but if you were accounting for this strictly, you would take into account that part of this is a prepayment. Accessories and miscellaneous expenses that I've bought for or spent on the car came to £346.13. This is for things like new wiper blades, bulbs, membership of the AA and IAM etc. MOTs & Services came to a total of £1327.88, but a large chunk of this cost was from one massive bill from Lindsay Ford - an expensive lesson on the virtues of shopping around.

Diesel
In 609 days of motoring, I've burnt 2238 litres of diesel, travelling 22500 miles, and an average MPG of 47 (maximum achieved was 55). Total cost is £2829.67. The price of diesel has risen steadily over the last 18 months as shown by the graph below.

Cost Per Mile
All things considered, motoring for me is costing me 29.5p per mile. This puts business mileage in a new light, since they only pay 30p per mile, it doesn't seem like such a boon anymore.

More startlingly, spread over time, cost per day is £10.87! Now, this doesn't account for the mileage given back to me from work, but this is a great deal higher than anticipated.

Bottom line is, travelling anywhere is costing me approximately 30p per mile. A lot of this is fixed costs that can't actually be saved by keeping the car at home - about 13p per mile is burnt up in Diesel. But the fixed costs should be attributed somewhere, and a per-mile basis is as accurate as I can think of that is practical to work out myself. So, put into real terms, 30p per mile means that's £4.60 every time I want to go to Ultimate Frisbee training in Belfast, £5.96 every time I visit Bangor, and £26.79 to visit my Grandparents in Armagh and (on a full cost per mile basis as outlined above) to take the car down to Cork for the Cork Open will cost £156! (£65 of this is diesel costs alone).

When I pay for things like insurance and tax or even diesel, it's hard to keep a grasp of precisely how much each journey is costing. If I keep this figure of 30p per mile in my head, maybe I'll walk a few more journeys, or dust off the old bike. This is a scary amount of money!