Sajou,
I'm attaching my sample file as well that you can play with but only after you read and do some serious work of what Ron has suggested in his post. It takes time to get a firm grasp around SL variables. Once you get that out of your way, you may even create a scenario based questions just like in my sample or even better than that. For instance, If you don't want to buy computer, the next question asked is if you want to buy a laptop instead. If you do want to buy a computer, the next question asked is if you want to buy a phone. If you choose NO to all answers your learner get notified that it did not buy anything and that the budget is still the same. The basic setup is to create a number variable called "total" with a value of your budget. All you have to do is to create a trigger that will substract another number (cost value) from the total variable when something happen (if something has changed the state or if something is clicked etc.).
https://360.articulate.com/review/content/c6670d52-8e10-4578-8589-03eee8a98b39/review
