Hi looking for some advise, I have just had a rear Abs sensor replaced on my audi Q5 the garage is not a main dealer and usually does work at a fair price however has charged me £300 for sensor replacement seems a bit expensive for a small part? 

Hi Alison, yes it does sound a bit steep, but firstly is your Q5 a quattro? If yes then it could be down to the ABS sensor being stuck into the hub and they have then had to strip the hub down  to get the sensor out without causing any damage to the rear CV joint, wheel bearing and ABS reluctor ring that works in conjunction with the abs sensor, ask for an itemised bill as to what they have done.

Hello Alison, 
As Daryl points out, although the sensor is likely to be externally connected, the sender/ signaler may be built into the hub, which may mean the hub has to be replaced.

Again, as Daryl says - ask for an itemised bill. 
Kind regards,

Gareth.