$150 is ridiculous but thats what the market demands, so it IS on par. you can get older ones with the square 4 for $80, newer ones will def' run you $120 and up, negotiate for $120 but chances are good the damand will make it so you'll end up paying $150. you sure SteveM is dry? he always boasts about his hordes of parts and ability to get any part, ive seen the pics, stacks of inserts. Maybe he thinks you hang out on rep forums trying to buy gen parts to put in your rep
a gen insert definitely looks better than any aftermarket i've ever seen, but $150 can buy a lot more of anything else. your sellers insert looks good.
as for my wm9 watch all I added was a better (clarks)crystal, and a gen insert ONLY because I had one from a previous project, if I didnt already have it i'd just use a WM one. what else does it really need?