Those flat cams seem to be a little more expensive than the tophat style....I've been looking at them on eBay for my 319 lately and people want a lot more for them than for the tophat style, and they aren't as many of them listed. But they ARE there, some large sets even, but those seem to be going for $40 or more.
I've never sewn on a 328 and I can't decide if I like the looks of it or not (it's a little like a pug, it might be so weird looking that it's cute but I haven't decided yet), but I definitely would have bought it for the price you paid! Around here, it'd have been a good deal at the original price!