That's not extraordinary for a complete job. Transmission removal and installation in an AWD vehicle requires more labor and additonal parts and supplies. It's rare to have the transfer case separate cleanly, and at a minimum will need 2 liters of AutoTrak oil and a front gasket. Further, for a truly "complete" repair your shop may replace the front seal in the case as well as the output shaft seals, and probably the mag drain plug.
As for the transmission itself, the wear parts are not expensive. A full clutch and seal kit can be had for less than 300€. If "hard" parts are needed the costs can increase quickly. Most professional shops will not warrant their work without a new torque converter being installed. You will want a new oil pump and separator plate at a minimum.
Then there is almost always some valve body work to be done, or a replacement valve body. That can be reasonably priced in North America, but I'm guessing that not many shops on the continent understand what needs to be done, let alone have the reamers, drivers, and pilots to repair Hydramatic valve bodies. At best, some BMW shops may have some idea since they used Hydramatic transmissions for several years, but even that is not as likely.
You might expect another 100,000km of service, and your routine scheduled maintenance certainly can't hurt, but eventually the trans will need some work. Hopefully, that provides some time for you to shop for a better option.
Of course, your can always do it yourself:
http://www.wwdsltd.com/4L60/4L60ERepairs.html