Every third burrito it changes it to 2.00 automatically.
It could be configured to calculate price differently too.
If that looks like it might work I will share what I did. So far I cannot get it to set price based on numberpad input yet. I an working on that.
EDIT: Got that to work
Was actually pretty simple just the 1 rule and 1 update order action.
Instead of each item you can probably use Menu Item Group Code if you want multiple beers with 1 constraint