Hi form a newbie. I don't want to provoke an argument (and it's my first post), but let me throw a different perspective into the mix.
A new CX 5 is somewhere mid £20k range to buy. It'll be worth about half that in three years, so it'll lose ten grand give or take (plus interest if applicable).
It'll need serviced a couple of times too, let's say £400.
It might need a couple of tyres too, lets say £100.
Maybe a set of front brakes, say £200.
You say you've done 1000 miles in around a month, so lets assume you'll do 12000 miles per year, and that let's call diesel £6/gallon.
12000 miles @ average 37mpg = 324 gallons, or £1944
12000 miles @ average 46mpg = 261 gallons, or £1566
Over a 3 year ownership the costs are:
Depreciation 10000 or 10000
Servicing 400 400
Maintenance 300 300
Road tax x 3 years 90 90
Insurance x 3 years 750 750
Fuel x 3 years 5832 4698
Total 17372 16238
Break that back down to average per month, it's £482 against £451 (and that's without paying any interest).
Obviously the above sums can vary drastically on how you buy/finance the car, how much you get as a trade in, how long you keep it etc etc, but you get my drift.
IMHO it's not the extra £31 of fuel that makes the difference, it's whether the four hundred and odd quid per month is too much in the first place.