I would say that the fact is 'saving' is singular and 'savings' is plural. This dictates the verb that follows. You could say A saving of $20 is ... or Savings of $20 are ...
A basement bathroom can be built for about $15,200, Fred estimates. Of that, plumbing is the largest component. These prices are based on costs for a small bath measuring about 6 by 8 feet, with 8-foot ceilings. However, many basements are limited to a 7-foot ceiling. Another potential cost-saving location for a new bathroom is the attic.
On this site you can enter the information about your home and the addition and you will get an estimate on the added value the bathroom addition will give you. In 2009 the cost of adding a bathroom into an existing floor plan would normally cost between $3,000 and $6,000 for the average do-it-yourselfer. If you enlist the assistance of a professional they will make sure your space meets code and will add labor charges to your renovation bill.