ncc98071

Hi

I have a 02 impreza wrx, and it is giving the follwoing error at the moment

p0031 HO2S Heater Control Circuit low

Presuming this is the O2 sensor that is gone,

If this is the case ,is it safe to drive the car until i get it repaired
where is the cheapest place to get a new 02 sensor
Would a seconhand one be any use?

Thanks