The first implementation was weak from the start. By exposing the instance variable directly, you threw away all the power of inheritance and guaranteed a future meltdown. If you had correctly implemented setters and getters from the beginning, you would have been perfectly prepared for what would have been a minor and appropriate change to the pricing scheme that are the whole point of encapsulation. You wrote procedural code using an object-oriented language. Don't blame a fundamental design approach for your lack of good implementation.

"a lot more code" - Really?