From a doctrinal point of view, SSNs essentially have unlimited range, so are also suited for global sea denial and power projection in high-end conflicts.
Plus if the cost of an SSN is about $1Billion, that is roughly the same as the Type-55.
So the cost doesn't seem prohibitive given how many Type-55 are being produced.
Also think what the existence of a fleet of 30 SSNs would mean.
That would mean 4 SSNs constantly patrolling the Pacific, which would significantly change the military balance of power.
It’s very unlikely a SSN can be attained for 1 billion $. A 041 costs 500-620 million $, the closest western equivalent, the Japanese Soryu, costs 536 million $.
If the 095 is performance oriented, it’s likely to cost more or about as much as the Seawolf class (6 billion $) which is equivalent to ~5 fleet destroyers. Even if it incorporates heavy cost saving measures, it would likely cost more than 3 billion $.
The cost is prohibitive compared to the use they would get.
30 is not that ambitious of a number through, on the high end but hardly a massive fleet like the US one. I could see them going with that, or 10-20 SSNs.
The current military doctrine doesn’t support contesting international seas aggressively, only retain a capability to hit weaker actors as an insurance. Having 60+ SSNs would benefit China if war and making tributary states were an important part of their economy, but right now it isn’t. That’s evidenced in the very low military budget.
One thing that’s certain is that the 093Bs are getting long in the tooth as the early 2000 boats they are... every other country has made new SSN since then.