obliged to give you a price upfront on request and cannot refuse to give you your car back!! Sorry for what has happened to you, i was a self employed mechanic, and i did MOT`s also, and would NEVER do work on a customers car without a price for them!!!
I would certainly question this and take it further, maybe to trading standards etc!
Sorry also, BUT you should have refused to pay on the grounds you were told it wouldnt be much!!!
Please take it further my friend, gives hard working independent traders a bad name!!