Can I create a udf function that performs a query, that returns a single row with a single field, and then return the value of the single column/record?

Here is what I have tried:

CREATE FUNCTION CaseResourceCost  (@meetID int)  
RETURNS decimal(12,2) AS  
BEGIN 
        Declare @returnValue decimal(12,2)
        select isnull(sum(cocasedata.itemunitcost * coCaseData.ActualQty),0) as avgResCost
	FROM dbo.meetings  INNER JOIN  
	             dbo.meetproc  ON meetings.meetingnumber =meetproc.meetingnumber INNER JOIN 
	             dbo.cocasedata ON meetings.meetingnumber = dbo.cocasedata.meetingnumber 
	             where meetings.meetingnumber = @MeetID

      set @returnValue= avgResCost
      return (@returnValue)
END

But I get the following error
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Microsoft SQL-DMO (ODBC SQLState: 42S22)
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Error 207: Invalid column name 'avgResCost'.
Select statements included within a function cannot return data to a client.
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OK
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