If he gets a smaller car, the road tax will be less. Mine is a bigger one, so it costs is £110 every 6 months, so think of that as £20 a month.
As Fedup says, MOT is around £50, although if you shop around you may find one for £35, and that's once a year. Then you've got the cost of any repairs needed to get it through.
We also use about £30 a week on petrol and do about 5000 miles a year, so you should be able to work out about how much you'll use from that.
I've always had older cars and bought them outright, but then ended up spending shedloads on repairs for them. So this time, we went to a dealer and bought a car that was only 3 years old on finance. Yes, I pay £115 a month over 4 years for it. But I have not had to spend a penny on it since I bought it - apart from a new wiper blade when I tried to use them to de-ice the car!!! And the piece of mind I have with young kids in the car knowing the car is a good one is priceless. I'm sure you'll remember my disaster coming back from Chester Zoo 2 years ago? 6 hours at the side of a motorway with a 9 month old and no milk wasn't fun!!!
Saying that though, my friend bought that car off me for £400 and she loves it and has only had to buy a new radiator in all that time!