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.
A 10-by-15-foot bedroom addition, for instance, might cost $900 to $1,200 just for framing. An addition that includes a kitchen will require plumbing and boost costs. An addition with a kitchen can run $250 to $300 a square foot, not counting finishing details like appliances and countertops. An addition with a bathroom can cost $125 to $200 a square foot, again with a number of cost variables including type of flooring, shower and tub, plumbing appliances or custom lighting. Decide how much you can afford and adjust your addition to your budget, then get a good plan.