Walker Healthcare, Inc. sells canes and walkers. Currently, it sells $10,000$ canes annually at an average price of $$20$ a unit. It is considering adding a lower$-$priced line of walkers which sell for $$49$ a unit. The company estimates it can sell $5,000$ units of the lower$-$priced walkers but will sell $250$ less canes and $500$ less of their expensive walkers sold at $$99$ a unit by doing so$.$ What is the amount of the sales that should be used when evaluating the addition of the lower$-$priced walkers?