How much would it cost to develop an entirely British fighter? Divide that across 150 . . .
The unit cost would be insanely high.
We don't have infinite amounts of money.
Lower numbers have been reported all over the place, but most report I've seen have ignored the future spending & batch purchase elements. You have to be careful when evaluating reports on defence websites. Most merely regurgitate press releases, & articles written elsewhere. The number with real reporting is very small, & mostly linked to the specialist press, e.g Janes & Flight. I've sometimes tracked back stories which have been on multiple defence websites to their sources, because I was suspicious of their accuracy, & found that they all derive from one source, which has an obvious error or omission in it. In one case, for example, someone on Defense Industry Daily had misread a Selex press release, & the resulting error had proliferated.
The "India to by Kittyhawk" story was on vast numbers of websites, but was pure myth.
Numbers of websites mean nothing: you need to go back to the origin.
Also, don't trust broadsheet newspapers on defence. Their reporters generally lack both expertise & contacts in the field, & the quality of editing of their articles is appalling, as editors know even less, & can butcher even the best articles into meaninglessness. Even the generally excellent FT prints nonsense on defence.