In reply to yorkshireman: Skate skis propel you forward by the use of the edge of the ski, so that the 'pushing' ski is on its edge (herringbone shaped tracks on the snow). Classic skis use either scales or wax to grip the snow, so that the ski base is flattened on the snow and the scales/wax are gripping the snow to allow you to push forward (parallel tracks on the snow).
Options: There are combi skis which combine the features/compromises of both designs. If you are happy skating on a classic ski, why worry about buying skate skis? Before dedicated skate skis were developed, the racers used classic skis to skate with...
Other thoughts:-
It's not unusual to use a different length of ski for classic, than for skating.
There is - probably - nothing to stop you applying grip wax to a skate ski, although it would - probably - never function as well as a classic ski...
The usual caveats apply. The major difference would be in using skate boots offering more support for the ankles while skating, rather than the lower-cut classic boots...again there are combi boots which combine the features.