The OP said that titanium was rejected for the MiG25 because it was too expensive, I don't know the numbers but the Soviet Union was a relatively poor country so that makes sense.
For the USSR I believe it's less the titanium being expensive (since it was the worlds largest producer with the only country that really started producing titanium a bit later in the Cold War being Apartheid South Africa (part of the reason why completely breaking relations with South Africa/really strong sanctions were so difficult and delayed by the US and other Western powers. Namely they had to deal with the South Africans to purchase the titanium needed by various high end weapons. The US had pulled the "Sneakily buy it in small quantities through shell companies from the Soviets" earlier but I believe they caught on and it really wasn't a long term sustainable option. That meant South Africa. )
The problem with building aircraft and other high end weapons from Titanium (like the couple of subs the Soviets built with Titanium hulls) is that especially at the time it's a really expensive and complicated material to make something mostly off. For the Soviet titanium sub if I remember correctly the Soviets had to build a custom one of a kind building slip in what was effectively a airlock with the air replaced by some gas highly toxic to people. Meaning that all the workers had to work in full blown MOP style protective gear with the possibility of even a slight tear in the gear meaning death for the worker. The cost of building that single sub was like the cost of building half a dozen more normal comparative SSN attack boats. I mean having to build a completely unique never done before building slip/atmospheric containment bubble filled with highly toxic gas to build a single sub (and that custom building slip was only a small part of the expense of the effort. I mean having to build a completely unique building slip/atmospheric containment vessel/gas chamber just to build a single sub is insane.
I'm just not sure a majority/almost all titanium construction Mig 25 would be poducable in anything above a Cottage industry level with probably about as many made as the US made SR-71s and the various related models. You'd end up with like two dozen interceptors.