I did this two-and-a-half years ago for our fifth anniversary trip. I was the first person in line in the morning, so we had no wait. It was a wonderful, memorable experience.
Picking the pearl plus a silver necklace cage came to a total around $70, I think. A little steep, but a special souvenir I've kept, obviously, and still wear today-- I'm not big on souvenirs in general, but this seemed worth it. If I ever did it again, however, I'd probably get a cheaper setting in advance.