Welding titanium is highly frontloaded. Designing the necessary equipment and testing the processes are the main cost drivers. The actual welding is not. Yes you will have to preheat it but that is still absolutely marginal. The Alfas used fourth generation breeder designs, which are a more likely problem, than the costs for producing a bit of steam. Automation again is highly frontloaded. Designing and building the machines is the primary cost driver. If done right they will be cheaper during operation. Hulls are not a primary cost driver for submarines. Sonar, propulsion, and weapon system are. The second Yasens price tag was $3.5 billion 50 percent more than the price you give for a newly built Akula. The reason why in each class the first ones (I guess you are right about the first Borei as in it also might have used a Akula hull) were so cheap is that they excluded everything but the work on the hulls and installation. Yeah super cheap in case you have a reactor and a sonar lying around.
Kirov had an reactor accident. There is no chance in hell that this ship will enter any navy again, ever. All 3 Boreis were supposed to be stationed on the Pacific to retire the Delta IIIs. The problems with Bulava prevented that. Two are with the Pacific fleet. Why do you always write one?
How am I wrong about Yasen. I am clearly comparing it to a to quote myself "newly built Akula". I don't care if you call it an escort or a fleet submarine as the British still do the role is clear, and Yasen is clearly designed for that role. Yes it would be good in pretty much any SSN role, but that wasn't the point. The point was that other roles could be filled just as well but significantly cheaper.
It doesn't help your case to quote somebody who might be a bit biased claiming no issues and then quoting an accident that sounds exactly like the scenario that I described, but was most definitely caused by some technical problem.
Anechoic plates can be easily adapted to absorb both sonar and radar. In the later case a wavelength up to twice their thickness. 30 cm could absorb everything shorter than 60 cm. AKA every single radar used either by US ships or airplanes. I bet they already are. Milkcows were targeted due to their danger as a primary target by the British. China is in exactly the same situation as Britain in their dependence on the ocean for energy. We (the European)would be too once we can't import from Russia anymore. This is of course based on the assumption that both sides would be reluctant to use nuclear weapons.