Declare @Id Int                               
Select @Id = Id From sysobjects Where Name = 'History_Price'
if not Exists(SELECT * FROM syscolumns WHERE id = @Id and Name = 'Price_Consumer')
  Alter Table dbo.History_Price Add  Price_Consumer MONEY NULL
  

Select @Id = Id From sysobjects Where Name = 'History_Price'
if not Exists(SELECT * FROM syscolumns WHERE id = @Id and Name = 'Price_Finish')
  Alter Table dbo.History_Price Add Price_Finish MONEY null