please advise thanks

hi can anybody help me i bought a audi 1.8 t sport a few weeks back and ive just had the back brakes done so while i was in the garage i had the car put on a computer cause i have been having lots of problems with the car . the main prob is its drinking petrol i mean 45-55 miles for a £10 (if this is normal?) anyway the problems according to the garage owner is that my turbo boost sensor and my coolant sensors are gone hes said that it will cost about £200 to fix? can anybody tell me is this right? regards alan