We dont have tooo firm a structure to be honest.
If someone is being classed as (counted as) one of the display crew then they get paid, while they are being initially trained they are normally "extra" over and above the normal crew numbers.
It's down to the individual how quick they pick things up, how useful they can be on site etc etc - we don't have a hard and fast rule that says "your first five displays are unpaid" or similar.
I'm afraid we dont have a "table" for crew rates, there are many variables regarding the site conditions, type of display etc etc but we do try to be as fair as possible
cheers
Stu