I have been asked the question a bunch, and the answer usually drives people away.
Due the the process I use to create the inserts, the ring/lip/shoulder would be a second process and solder job. This adds to my time, and therfore to the cost of the insert.
Even if I just charge an extra $10 to machine the shoulder, solder and then machine it to final form, most people are unwilling to pay $40 per insert. (As it stands, by business advisore is furious with me... The inserts should actually be $48 each, according to her calculations and standard shop rate... No one tell her I am still selling them for $30
Now, the reality... If I spend another 15 minutes... That means $15 plus material used (We will call it $0 for now, as I would have to work it out before I can get a reasonable figure) We are talking $45 per insert.
If that figure is acceptable, I will be more than happy to eat the material, and do the work.