As a maker of slipjoints I can attest to the amount of time that goes into a quality single or multi-blade slipjoint. I made fixed blade knives for 4 years before making the commitment to make slips. I try and make my knives true to the older patterns and as such, a fair amount of time, materials, research goes into these little knives. I truly believe that the prices offered by the lesser known makers (myself included) represent a very FAIR value in handmade knives.
I do not know if you have had a chance to handle many quality handmade slipjoints(OP) but if you have or will in the future, I am sure you can appreciate the complexity, design, material, craftsmanship that makes up a slipjoint. Thanks for your valid question!
Ken