I made a list:
Orange fencing (ie. from construction) can be used.
Pros,
Slides fast. therefore doesn't require huge hill
Cheap
Easy to "steal"
Cons
NO edge hold (like turns)
You can still hit rocks
Needs a little water
Hard to make a jump (need some wood and put fence over it)
Will dirty you, and your skis with mud
Rugs/Carpets
Pros
Cheap (if you go around rug stores asking for samples; otherwise.....)
Better edge hold then orange fencing
Won't get skis/you dirty when falling
Cons
Rug burn when falling
Requires soap/water
expensive
Snowflex
Pros
Closest to real thing
Cons
rug burn when you fall
Mighty expensive and hard to aquire
I use orange fencing and old skis. Or you can rollerblade (much easier to do).
