Hello Reptil,
giving advise on how much equipment should cost, something I do not want to answer, because the market sets the price, and what is the stuff worth to you, etc...
However talking about respectable, the seller should tell you that the V72a and V74 are not mic pres or better no input modules like the V72.
V72a and V74(a) are nearly identical, build upon the same chassis/components with minor changes in final wiring, the V72a falls with the V72b and t into the buffer amp category, designed with 34dB make up gain for passive elements like filter, fader, pan pots, etc.
Using them in a kind of mic pre set up works somehow, but does not sound like the V72 at all, or like a good tube mic pre should.
The V74(a) however works very good as a line driver, I use several myself for splitting signals and driving cables 400 meter plus, but sucks pretty bad on your front end....
If you are looking for a real good mic pre sound a la V72 or V76, save some more money and get the real thing, you won't regret it. (please keep in mind that you need to get it rebuild)
If you are in the market for a good mic pre, the Neumann sounds very good for being an op amp based unit, probably the best choice in your situation, due to some design/manufacturing problems with the V72a/74.
During the time they were designed several material improvements were made, PVC foam vs. the natural rubber found in the V72 units, hot glue vs. metal screws, etc. This worked very stable for about ten years, but than in the mid 70s most of the improved materials turned out to decompose much faster than the older materials used and while doing that destroying the wire insulation of the x-former, resulting in compromised sound or an open winding.
Nearly all V72a units and every V74(a) that people send to me had problems with the x-former. Rewinding is a costly option, replacement versions available sound pretty 2 dimensional....
Hope that helps...