mjwman’s post gives the impression that his wife buying a brand new Sandero for £3,564 (£99 x 12 x 3 = £3,564), obviously she is not.
Most of these, small deposit and X amount per month for three years deals involve you paying off half the cars value in those three years; you then have the option to buy the car (for the remaining balance), or walk away from the deal – having paid half the value of the car to drive it for three years.
I doubt that anyone will sell you a new car at £150 per month for three years of payments (total £5,400) – other than on the above terms.
My advice is to see if you can find a good pair of new trainers.