Well, I picked up the serger yesterday and the experience was much more positive than I'd anticipated. They explained what was wrong, returned the broken part to me so I could see it, and provided samples serged with my machine to show that it's in good working order. The woman who was at the desk was the same woman who had taught my "learn to use your serger" class a few years ago, and she was as lovely as ever.
I did a little research and found that their service cost is the same (or better?) than other places in the city. I also found out that the cost of the repair was included in the service fee, I only paid extra for the part. And, upon bringing the machine home, it's serging charmeuse like a dream without so much as a single tension adjustment. Win!
So, all's well that ends well. I guess I'll just chalk it up to a slightly over-aggressive saleslady (or, perhaps one who just has a very different sense of value than myself.)
Now, to find out if the Pendrell can be rescued. Here's hoping!