Validation based on score?

Hello Qualtrics community,
I am currently working on building a survey that simulates spending on a shop catalogue. I've set it up so that its a multiple-answer multiple choice question with scoring to simulate cost of each selected item.
Participants have a certain budget - and I'd like to have it so that they can't proceed in the survey unless they fall within their budget (e.g., selected choices resulting in their "score" or "spend" has to be less than 1,000).
Ideally, I can set up custom validation based on embedded data / scoring. But Qualtrics doesn't have this basic functionality. Can anyone help with a solution?