Do I have it right, that based on discounts and research cost inflation, the optimal research path looks somehing like this:

- get Instruments ASAP for discount (should be your second purchase)
- next buy a level 3 and level 4 tech, in that order, to unlock level 5
- buy all level 5 techs
- buy all remaining level 4 techs
- continue, with 3, then 2, then 1

This should let you buy the most expensive techs before inflation impacts them too greatly, total should be somewhere around 11000 research cost.

By contrast, if you save the level 5's for last, you're spending well over 20000. I'm not sure how much more, I didnt run it all the way through. Thats even if you still get Instruments as your second purchase, but otherwise buy things in order of low-to-high.