Last Friday, I had lunch with Augsburger and Zippy. Then I visited my sister next door in Thousand Oaks
First we went to CostCo. They had no cable modems. Walmart was just across the street so we checked there. They had what I wanted, but it was at the online price. I asked about price matching and the manager seemed confused by the question. Eventually he decided that Walmart does price match but doesn't include any on line prices, including Amazon.
Saturday evening I order a Motorola SB6121 from Amazon for $77.44 with free shipping. It arrived today. Tomorrow, I'll call Cox and swap the modems out.
Thanks everybody for your advice.