Establishing referential integrity in a generic table?
You can use this design, which requires one more table:

 - DropDown:
     DropDownID  PK, 
     Name nvarchar(25)

 - DropDownOption: 
     DropDownID  FK (DropDown)  UQ1, 
     DropDownOptionID  PK       UQ1,
     Name nvarchar(25), 
     Description nvarchar(155)

 - Estimate: 
     EstimateID  PK, 
     etc.

 - EstimateOption: 
     EstimateID  PK,   FK1 (Estimate)
     DropDownID  PK    FK2 (DropDownOption), 
     DropDownOptionID  FK2 (DropDownOption)


For every row in Estimate, you'll have to add (up to) 13 rows in the EstimateOption table (one for each dropdown menu).

The additional Unique constraint in the DropDownOption table is needed for the foreign key (FK2) from the EstimateOption table.

What you have in your current design as Estimate, can then be constructed with a pivot query from the two tables.