A quick question related to Amperex Bugle Boys

Some info about the original question. I think the 5AR4s were made in England in the Blackburn Mullard factory but were sometimes labelled Amperex. Phillips was a Dutch conglomerate that owned many tube brands, Mullard, Amperex, Siemens, Valvo, and on and on. Tubes made in one factory could be labelled with the brand of a different factory. The way to tell where and when a tube was made is to check the codes etched into the glass of the tube. here is a list of the codes and how to interpret them:

Phillips Factory Codes

Any tubes you come across today will be "New Code’ so just ignore the ’Old Code’ stuff. Also etched tube codes can be hard or impossible to read, but that doesn’t necessarily mean the tube is a fake.

For example look on page 11 of the linked document for a lower case f and 3, f3 and you’ll see that’s the code for a GZ34 (AKA 5AR4)

There were also many other tube makers who had their own way of identifying tubes, for example, Telefunken, RCA, GE, etc.

Yes you are correct. Almost impossible to fake the acid etched codes. After a great deal of experience, you become aware of the internal structure of certain types from certain manufacturers. Even the thickness and shape of the glass become familiar. One of my greatest irritations currently is the contention that Sylvania Bad Boy 6SN7s extend beyond the true bad boy which is a very distinct tube. 

Assuming that this can be considered a high price for a dual triode (stereo) preamp tube relative to its NOS availability, when might someone attempt to perfectly clone this Amperex tube?

There are fake Bugle Boys out there already.  Along with fake just about everything else.  They are not that common though.  As @audition__audio  said  if you have a lot of experience with tubes, more than I have, you can spot fakes by examining the structure.  They don't make them like they used to.