Would something like this work?
let money = parseInt(pm.collectionVariables.get('money'))
pm.collectionVariables.set('money', money - 200)
Not been able to run this yet so I’m just giving you a quick idea 
Would something like this work?
let money = parseInt(pm.collectionVariables.get('money'))
pm.collectionVariables.set('money', money - 200)
Not been able to run this yet so I’m just giving you a quick idea 