I'm in Laguna Beach. I had these axles made years ago and probably still have a spare/extra set. As I recall I probably paid a similar amount to what you mentioned. Also, look at OKP in Germany - they sell them as well.
After searching threads for 15 spline axles, I finally found yours.
I'm looking for axles just like he ones you had made.
I have a 15 spline ZF that I would like to put into my '64 Giulia Spider vintage race car. I have some original 15 spline axles (solid, ot gun drilled) out of another car with unknown history. I'd prefer to use some 4340 like you had made to make it a 'forever' fix. Mark Williams can make them for about $450/axle which seems like a lot.
Any info/guidance would be of help.
I'm in San Diego.