I appreciate all of the advice and suggestions! There must be hundreds of different models of InSinkErator-made disposals, based on a couple of days worth of research.
Many chain stores carry slightly different models so that you can't do a direct price comparison. Menards has their own brand, "Evergrind by InSinkErator." (Link below.) Their 3/4 HP version appears to be a clone of the Kitchenaid 3/4 HP model, and it is on sale for $188. I purchased it and will give it a try.
It has a stainless steel food chamber and grinding components, and a dual-stage grinder that is supposed to grind finer, which may be better for older plumbing like we've got.
Naturally, replacing one item has led to a cascade of replacing other items.
Our kitchen sink is a circa-1998 Americast by American Standard, an innovative idea that turned out to not be a very good idea, of making a lightweight version of a cast-iron sink. It looked nice up until recently. We actually got decent life out of ours compared to some people, according to searches on the internet. Ours is chipping around the edge where it meets the counter, rusting and warping. It will be replaced with an 18-gauge stainless steel offset sink.
Since the sink is getting replaced, I decided we may as well replace the old Moen faucet with a new one. The old one doesn't operate smoothly and is corroding a bit around the base. Apparently those new combo faucets with the pull-out spray head are popular, but they look gimmicky to me. Anytime I've ever had a problem with a kitchen faucet, it's been with the sprayer. I'm going with a new Moen that has the separate side sprayer, like before.
Although I've installed garbage disposals, sinks and faucets in the past, I really don't have time right now. A plumber is scheduled to do the job on Tuesday.
The old garbage disposal was a Kenmore I purchased and installed 17 years ago, and we certainly got good service from it. It has always been loud, though. I'm looking forward to something a bit quieter. The kitchen is completely open to the dining room, and the disposal, when on, drowns out conversation.