Hey, i played around with the planner a bit and managed to reduce the building costs of a few reactors from the first page. (at least in UU Matter)
Beginner reactor 2
new
Copper: 197 -> 175
Tin: 19 -> 17
Iron: 68 -> 73
=> UU Matter: 169.83 -> 167.46
Mid level 1
new
Copper: 399 -> 410
Tin: 63 -> 62
Iron:207 -> 201
Gold: 24 -> 20
=> UU Matter: 430.96 -> 422.17
High efficiency zero running cost reactor
new
Copper: 625 -> 598
Tin: 91 -> 88
Iron: 279 -> 272
Gold: 34 -> 28
UU Matter: 613.32 -> 587.98
Also just a slight rearrangement already saves 2 component heat vents.
They're no big improvements and probably dont matter when you're far enough to build most of them. But you never know, when it might come in handy