Walmart offers the Fluidmaster Toilet Tank Fill Valve, model no. 400A, for $6.34. Opt for in-store pickup to dodge the $5.97 shipping charge. That's the lowest price we could find by $3, excluding the mention below. It features corrosion-resistant materials and replaces flat ball and rod assemblies.
A close price: HD Supply has it for $6.64 with free shipping.
There are many ways for seniors to get cheap -- and even free -- entertainment and services.