Preventing Budget Overrun

I found a gap in testing where the user could "trick" the system. I'm thinking "maybe" a Formula query could help, looking for insights. 

Use Case. The user enters a value of 11 hours on a budget of 10. At this point, [Save & Continue] button is hidden by a form rule, and in it's place an [Update] button is required to save and redisplay the record in edit mode. If no Alerts exist, [Save & Continue] is visible. The problem being that at this point, the user "could" opt to edit the hours again, and potentially those hours could exceed the budget as shown below because [Save & Continue] is visible. 

I modified the button formula as follows to redisplay form 1 which is 16 instead of proceeding to form 2 which is 20.

var text DisplayFormInEditNoAlerts =
If([Active Form]=1 and [Qualifies to Show Save & Continue]=false,
URLRoot() & "db/" & Dbid() & "?a=er&dfid=16&ifv=1&rid=",
URLRoot() & "db/" & Dbid() & "?a=er&dfid=20&ifv=1&rid="
);

Maybe the simplest solution would be to take them to Form 2 and use a rule to take away buttons and present the alert with the only option to go back, and let the form rule 1 lock them into place; however, a more pristine solution would simply refresh using the above code. The problem is that even feeding up a budget warning with a relationship doesn't work because it is not real time with the task budget until it saves.

I'm curious if a Formula query would be more dynamic/real-time? If so, what would be a good syntax for looking at Units delivered on the task table from the current DSR?