I found the ad the Harvey Norman catalogue (Brisbane) but there's no information of how much each previous model is worth.
Also found the same ad online.
https://salefinder.com.au/6216/computers/tablets/ipad-air/62…
"Trade up to iPad Air. Get up to $290 towards a new iPad when you trade in your current iPad. "
Sorry for crap details. Posted on phone
Strange that there are no specific details.