I'm sure the Typhoon's combat radius can reach Taiwan from Okinawa easily, but not to China's interior. PRC has strategic depth, Taiwan and Japan doesn't.
There are many articles on Typhoon's cost over-runs on the web. I suspect the Saudis got a discount on their purchase. I'm also not convinced that Japan would buy the Typhoon. The Japanese may leverage Typhoon in a competition to extract better deal from the US, and the US would do much to keep S. Korea and Japan within its arms export sphere.
In the unlikely event that Japan does buy the Typhoon, they'd probably end up with air-defense version (improved Trench I?) that can fire harpoons. This is due to Japan's SDF "self defense" policy of no strategic bombers.
At this point, the chance of Typhoon, Rafael, or even F-35 being exported to ROC is near zero.
It's realpolitik. We're moving OT so I'll make it short. IMO sooner or later Japan will lean toward a realistic/practical policy, shifting from using Taiwan as means to contain Chinese "expansion" into the Pacific, to accepting China's "entry" to the Pacific as inevitable. They'll seek to cooperate where possible and agree to disagree otherwise. Thus whatever combat jet the Japanese buy is irreverent in the long term, as Taiwan cannot depend on them for defense perpetually.
ROC/Taiwan must find its own way to deal with the status quo, instead of relying on table scraps and bread crumbs from the US. If the government had funded AIDC better for IDF upgrades, we'd probably see better quality, super-cruise capable IDF's (TFE-1088-12 engine) flying long before the F-16 C/D is ever delivered. Instead, AIDC had to fight for mere millions for small upgrades while the government throws billions at foreign imports. ;p Where's the love for domestic industry?
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