I need a formula that calculates the value of each field, multiplied by their different rates, then added together. If the value is less than$125 then show $125 if its higher then show the calculated value

Yes you could try something like this which if either Value is null it will show 0.

IF( OR(ISNULL(Value_1__c),ISNULL(Value_1__c)) , 0,
IF( ( Value_1__c * Rate_1__c) + (Value_2__c * Rate_2__c) < 125,
125,
( Value_1__c * Rate_1__c) + (Value_2__c * Rate_2__c)))

Kev