I've worked in similar scenarios and advocated for the Safari subscription. The most obvious problem with the physical book solution is that not everyone can read the same book at the same time. In my experience it's very common that, because some topic is particularly relevant for the team, many people will want to read the same book. At the same time, you do not want 30 copies of a book that was read by everyone 3 years ago sitting on the shelf.

And, as far as expenses go for a research institute, $4k/mo is very inexpensive.