The vignettes as they are called are now £28.50 Each, as you need two, one for the car and one for the caravan.I used to look on Ebay but people seem to get carried away and there seems to be no saving doing it that way.
Now In theory if you are good with a map and are willing to lose some time, it is possible to cross or move around most of Switzerland without using the M/ways and therefore not need the vignettes. But it wouldn't be easy....