What is the cost to repair or replace the head gasket and O2 sensor on a 1997 Honda Civic EX?

Not CheapSorry to say this ain't gonna be cheap for you. you are talking about 8 hours manual labour, the cylinder head needs to be presure tested to see if there are cracks in it & skimmed. ur talking about £400 - 500 just for someone to look at it.

i had so many problems with my 95 civic.

find urself a cheap reliable mechanic. if you live in Scotland i may know a guy that could help you.

cant help u with the O2 sensor.