I don't want my look up values to change...

I have a form that my users have to supply a cost code and a total dollar figure they are requesting. So to help them make sure they are staying within budget, I created a drop down of all their cost codes, a look up field for their remaining budget and a formula field that will push the user to get approval if it exceeds the budget. 

The issue is, that as funds are spent, the remaining budget changes and at some point will show that the requested amount is over budget, and force it to get approval, even though this request would have already been processed. 

How can I have this information display as a snapshot of the information at the time, but then not change as data changes. 

I hope that this is clear :)

Thank you,

Brandy


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Brandy Nunes
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