I think if you have to run a car anyway, then it is usually cheaper to use it all the time, rather than public transport.
I think (for a small, cheap car) you have to reckon on about £2,000 a year in costs, not including petrol, repairs or parking, just the cost of owning it. More expensive cars will be more.
It's true that a fair amount of that £2,000 will be depreciation in the value of your car.
When we had a car, it was definitely cheaper, especially when more than one person was going along, to take the car into town and park on a street with free parking than pay over £4 each to get the bus.
But now we don't have a car at all, and it will take a fair few trips into town over the course of a year to add up to the £2,000 we'll have saved just by not owning one, let alone the petrol costs we have saved over the past few years.
DH has a short commute to work by train, and spends about £50 a month on it, so £600 per year. I get the bus into town once or twice a week, maybe spending £300 a year. That still leaves over £1000 for longer trips every now and then before owning a car even starts to be comparable financially. That's nearly £100 a month for family days out by train - we don't spend anything like that much, and we quite often have a day out on the train.
We do need to allow more time to make journeys, and it is frustrating at times having to rely on buses and trains - but I'm convinced that we are actually saving money by not having a car at all. And the DC have amazing stamina for walking, which I doubt they would have if we could take the easy option of jumping in the car more often (I know I would take the easy option
)
If we do need to have a car again, we'll have to buy one first
- we'd probably buy a used one, but I'd be budgeting about £6,000-£8,000 for one, so we'd certainly be doing anything but saving a fortune.