O2 Sensors & Ignition coils
 

My vehicle is 2000 volvo s80 T6.It has 105k miles.I recently went to mechanic for servicing and he said the timing belt and waterpump has to be replaced for 105k service and he said one o2 sensor in front and one 02 sensor in back are damaged they need to be replaced and the sensors cost is including the labor $750.Can some one help me is these sensors replacement will cost this much?Or is there is anyway we can do that my self?
I really really appreciated for your feedback.

And one more thing last year i replaced all ignition coils and now this mechanic is saying one ignition coil#3 is not working fine it has to be replaced immediately which coasted is $160.How oftenly we need to change ignition coils?

The coils will usually last longer than that.

Buy Bosch only direct fit sensors. They are a pain but you might be able to do them yourself.