How do you reference cell value which will be deleted?

Need a macro that creates a formula in a cell.

As an example, cell A1 has a dollar amount. A2 is blank , but will have a dollar amount added later. Need the macro to put a formula in A3 that puts the dollar amount of A1 plus reference to A2. A3 will look like this, where the value of A1 is $234: 234 + A2. After the macro runs the dollar amount in A1 will be deleted so reference to the cell won't work.

When a value gets filled in A2, A3 will reflect the total of 234 and the value of A2.

Thanks, Cliff