Horn speakers for vintage sound

GIP drivers are extremely expensive, nothing is in your stated price range and they rarely come up for sale used.  GIP drivers are in the same price range as original WE drivers.  Also, they do not so much as try to reproduce WE drivers that employ permanent magnets, all of their drivers are field coil drivers requiring a power supply.

Great Plains Audio makes various reproduction drivers including close of Altec drivers.  They might be of some help.  https://greatplainsaudio.com/

You will probably have to hunt round on the used market and it will not be that easy, absent a lot of experience, to find components that match up well and to build a system.  It will be hard to find woofers that are high enough in efficiency to do justice to a high efficiency compression midrange (if you used an Lpad to drop the volume of the midrange driver, you will be wasting the efficiency of that driver).

Good luck.  

While it sounds like you are looking at traditional horn-based high efficiency systems (compression midrange and horn, plus other drivers for bass and tweeter), there are other approaches to similar kind of sound (very lively and engaging, particularly at lower volume), that are more budget friendly and great for someone who is handy at building gear.  There are some quite decent full-range or wide-range drivers that can be used in multi-way and even single driver systems.

Until fairly recently, I have never heard single driver conventional dynamic speaker systems that did not have a few shortcoming that were show stoppers for me.  But, I have now heard quite satisfying single driver systems.  Some could be assembled as do it yourself speakers by someone who is good with wood working.  I particularly like some of the 8" and 10" full range drivers in "quarter wave back-loaded horn" systems (look at Charney Audio for commercial system using that approach).  While the tapered horn of the Charney might be hard to do, there are simplified versions that work quite well like the "tapered quarter wave tube" cabinet (also often described as "TQWT").  While some of the better 8" and 10" drivers are not that inexpensive as new drivers (e.g., AER, Voxativ, Cube Audio), there are cheaper alternatives out there (e.g., Tangband) that work quite well.  

I have not heard any Shinjitsu Audio speakers myself, but, I find their design fascinating and the price is reasonable.  Their speakers utilize a horn midrange/top end and a back-loaded quarter wave woofer of small diameter.