Depending on where you live it's different. Also it really depends on your shows. If your showing in a A circuit show here in America they lowest they have is the puddle jumpers which is 2'6. I really don't know about other countries so I would just do some research about your country as well as the shows around you. Hope this helps :)
At the jumping shows I've been to, the classes with the smallest jumps would be cross rails classes (typically set around 1'6", the equivalent of 18in). The lowest vertical course is usually 2' (usually labeled as Beginner).
Hope this helps! Have fun and good luck showing :)