I have a ZALURE GUN with no special that I could sell. I think they go for 16-20+ PDs. I don't know if different episodes have different prices. Never made one myself.
I just got a PM and I have to say... I'm surprised by the high price. 18 PDs seems like a lot to me for the amount of hours needed to complete a Challenge Mode run - I have to admit that I expected something around 10 - 12 PDs. I'd love to complete a run by myself (haven't done one in years), but it is so hard to find a team nowadays...
I guess the fact that barely anyone runs C-Mode these days makes the prices go up?
Both sides, in my opinion, had some valid points. I'll see wether or not I'll get an S-Rank at that price, but I now at least understand why it was increased.