Hi Naveen,
Thanks for answering those questions. You know what, I spent 15 mins and had drafted some response including a logic that I previously implemented at my current client. But, I just scratched all that and came up with a simple solution for you. 
Just create this Dimension object (with the below) code in the Select clause in the Universe, it has prompts for Amount Spent for each month. When you try to parse it, it will give you an error that its not associated to any table, just associate it with the Calendar table and that should do. And objviously, pull this Dimension object in the Result Objects of the Query panel.
Replace the Reporting Date/Reporting Month Name with the Folder\Object name for Reporting Month Name. In my case, Reporting Date is the folder name and Reporting Month Name is the object name and add the case statements for remaining months.
Case
when @Select(Reporting Date\Reporting Month Name) = 'Jan' Then @Prompt('Enter Amount Spent for Jan:','N',,,)
when @Select(Reporting Date\Reporting Month Name) = 'Feb' Then @Prompt('Enter Amount Spent for Feb:','N',,,)
when @Select(Reporting Date\Reporting Month Name) = 'Mar' Then @Prompt('Enter Amount Spent for Mar:','N',,,)
Else 999
End
I'm 95% positive, this is going to resolve your issue, 5% is that you'll have to make these prompts optional as I don't know if your users are willing to enter values for 12 months every time they run the report and they may/may not be pulling data for all 12 months. And, I don't know if this Numeric prompt can be made optional.
Let me know if this helps and/or you have any questions.
Thanks,
Mahboob Mohammed