A new Mode C txpdr can be bought for under £1000. I don't nescessarily agree with forcing people to fit Mode S if they have a servicable Mode C transponder but I am of the view that the majority of aircraft should have a transponder. If not we'll be regulated in other ways (airspace for example).
Actually, (Rod will correct me on this) you can't now fit a new Mode C, only a secondhand one.
Since March all new installations are supposed to be Mode S and they are not available at less than £1800. Some who have fitted Filsers have now found they don't work and there is an AD on them
Our dear CAA have been telling us for some years that Mode S won't be mandated unless and until there is a low-cost low-powered version at less than £1000- they are starting to rat on this, as industry is not playing ball