It's a bit imprecise, but as I stated at the top "there won't be any divided by 100 or +/- 1 in the equations.".
TECH_FUTURE, TECH
Base cost = 960359
Beeline will always be zero for the last era tech(s).
( iResearchPercent EraInfo ) This is actually the starting era chosen, I gave wrong information about it in the post I quoted above, I will make an edit to it and add a bit more details to the equation while I'm at it.
It ↑ is as Raxxo said set to not modify regardless of era chosen as start.
[Base tech cost] = 960359 * 1 * 1.7 = 1632610.3
Duel / Normal / Settler
1 + [Cumulative Tech Modifier] = 1 + [ -0.5 + 0 + -0.4 + 0 ] = 0.1
[Tech Cost] = 1632610 * 0.1 * 1 * 1 = 163 261 (Close enough, the dll does it in many steps where it rounds the numbers in between.)
Gigantic / Eternity / Deity
1 + [Cumulative Tech Modifier] = 1 + [ 1 + 0 + 0.5 + 0 ] = 2.5
[Tech Cost] = 1632610 * 2.5 * 20 * 1 = 81 630 500 (Close enough, the dll does it in many steps where it rounds the numbers in between.)
I will add the missing "+1", that obviously confused Raxo, to the original post.