Sounds high to me? PMs around here go for mid-3s, which would make the stock a $300 add-on? I have read alot of reports of dissatisfied users of the factory folder, including alot of cut-up fingers and other body parts (sounds like sharp stamped metal parts edges?).
IIRC, the PM 18.5" takes 4 in the tube, plus up to 2 more with an extension. I've got a Vang Comp extension, which is extremely well made, and installed one of the <$10 aluminum followers from Brownells. Both highly recommended.