This was something I did a few weeks back with a group of Elementary students. It could probably be adapted for your students without too much trouble.
We spent a couple of days talking about types of shop and what you could buy from them. I then gave them a time limit and sent them off into the local shopping centre in pairs. They had to decide what they would spend their £100 on and take photos of each item. The pair who got closest to £100 and had the best reasons for their purchases were the winners, as decided by the other students in the group. They really enjoyed it and I hope your students do too
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