"Willie: Thanks for those links. Very nice. I was not able to get a sense of cost at the manufacturers sites."
There's a price spread, with short ones costing less and the long ones more, and with the barrel quality, caliber, and other finishing features reflected too. A generic short one might be $500, while a long one with a Lothar Walther barrel might run up to $2000. Bear in mind that these are often placed into top quality shotguns and the owners expect 1/2 MOA out of them after the inserts are installed.
Frankonia is a large retailer of shooting accessories, etc., in Germany and has a sales page where you can see a few wit prices. This is only a very tiny sample of what can be bought.
http://www.frankonia.de/Einstecklauf/Ansicht.html?Artikelnummer=96051
K+S is my go-to supplier. This is a good staring place:
http://www.einstecklauf.de/classic.html
Just take a look as the calibers offered. Then click on the links at the top of the page and look at their other product lines. Amazing stuff.
The German paradigm is that a hunter can buy ONE weapon for his hunting needs. Very often he either buys an interchangable barrel system where he can plug and play barrel assemblies onto one receiver, or buys a Drilling or combination gun. Sticking to the simple combination gun, in todays marketplace these are generally a shotgun over a rifle barrel. 12 gauge and say 9.2x72, which is roughly equal to any of the good .35 caliber centerfire rifle calibers. The hunter will then buy an Einsteklauf for the shotgun barrel in a smaller caliber cartridge, say... 5.56mm x ? for shooting small game, etc. This might be rimfire (.22 Mag is very popular there), or might be a .22 centerfire of some sort.
Going further, depending on his hunting habits, he "might" get his combination gun in something smaller, like 16 gauge and 5.56mm. But what about that hunt where he wants to take larger game? Well, he buys an Einsteklauf in some large caliber rifle cartridge for his shotgun barrel and goes hunting. Might be .30-06, might be 9.2x74, etc. he expects this adapter to shoot as well as the other rifle barrel, and he expects to be able to adjust ot so that both barrels shoot to the same point using a scope. These are not the el-cheapo inserts that we see here. He's probobly got a Zeiss or Kahles scope and he wants the setup to *shoot* using the insert just like it does without.
A pair of them, obviously, placed into a suitable host shotgun with decent sights *is* converting a shotgun to a very capable double rifle.
In my case, I like Drillings. Their advantages to a hunter are manifest. Double 16 guage with a 8x57JRS rifle barrel gives you great upland game shooting as well as a great deer cartridge. My Sauer shoots it's left barrel to point of aim of the rifle barrel using Brenneke slugs, and I've got a claw mount Kahles scope on top. Want to hunt deer? Load up rifle, slug in the left and buckshot in the right. Or... stick an Einsteklauf in the right and have rifle, slug, and a barrel waiting for that squirrel that's been chattering at you all day while you're in your tree stand. At the end of the day pop him and you can at least have a sterw while you contemplate tomorrow. Headed out for bear? Well... drop a 9.2x74 Einsteklauf in the right barrel, a slug in the left, and a nice hollow point in the 8x57 and press on. Weight? Just at about 7.5 pounds *with scope*.
You can build up a VERY nice system using these and a *suitable* host shotgun. Want a nice one? Start off with a nice old used prewar Sauer shotgun at about $800, add one or two einsteklauf tubes, be sensible about the sights you add, and you've got a VERY VERY fine system.
The one feature that Drillings have that the shotguns don't is that the selector for rifle/shotgun (between rifle and the left barrel) is a tang mounted slide that looks like a tank mounted shotgun safety. It isn't... it's a selector. Push forward and two things happen: You select rifle and amazingly enough the rear sight pops up out of a recess where you never even noticed it before. Slide it back and the sight vanishes. Magic. Good prewar German Drillings can still be had for about $2000 if you search a bit. The last one I bought (three weeks ago) was a Sauer in 16 guage and 9.2x72, with a claw mounted Kahles Helia variable scope. Condition NRA antique very good. Price? $1900. The one before that was a Sauer 16 guage and 8x57JRS with a claw mounted postwar Kahles fixed power 4, with a .22 mag einsteklauf thrown in to make the deal. It was $3200 complete with 2 boxes of loaded ammo and 3 boxes of once fired brass. Not cheap, but... superb.
The only challenge I see when taking a suitable shotgun (I'd personally use a prewar Sauer 16 guage) as a host is putting on pleasing and functional sights. Solve that, add a pair of einsteklauf's and you would have a beauty.
Willie