See the ADA FAQ at http://www.ada.gov/q%26aeng02.htm
Here are a few of the questions and answers:
Q. Are there any limitations on the ADA's barrier removal requirements for existing facilities?
A. Yes. Barrier removal need be accomplished only when it is "readily achievable" to do so.
Q. What does the term "readily achievable" mean?
A. It means "easily accomplishable and able to be carried out without much difficulty or expense."
Q. What are examples of the types of modifications that would be readily achievable in most cases?
A. Examples include the simple ramping of a few steps, the installation of grab bars where only routine reinforcement of the wall is required, the lowering of telephones, and similar modest adjustments.
Q. Must alternative steps be taken without regard to cost?
A. No, only readily achievable alternative steps must be undertaken.
Q. Will businesses need to install elevators?
A. Businesses are not required to retrofit their facilities to install elevators unless such installation is readily achievable, which is unlikely in most cases.
Q. When barrier removal is not readily achievable, what kinds of alternative steps are required by the ADA?
A. Alternatives may include such measures as in-store assistance for removing articles from inaccessible shelves, home delivery of groceries, or coming to the door to receive or return dry cleaning.
The ADA is very well written and did not become a fundamentally outrageous burden on our economy. All it has done is improve access for people with disabilities and really, all of us.