I am comparing costs of 2 ways to build a fluid Reactor, up to the liquid heat exchangers. While I will show Stirling engines, there should be room when properly built to add boilers and turbines or any other heat-needing device.
Here's the "Mutant Corner" fluid reactor. The top shows the placement of Fluid ports; the bottom shows heat exchangers and distributors. Every 6 Heat Exchangers need 3 distributors and 4 ports.
(I call it the "Mutant Corner" reactor because the corners of the reactor kind of "grow outward".)
Here's the ordered high-distributor reactor. The first pic shows the side, needing 3 distributors for 12 (or more) heat exchangers. The center is the distribution, while the top and bottom exchangers are returns. The second picture shows you can stack these linearly, 3 distributors to 2 heat exchangers.
To do 12 exchangers, (close to) the normal amount for a high-functioning liquid reactor, these are the key differences in materials. I'm ignoring the heat exchangers or other items as being equal in either case.
Mutant Corner reactor:
8 fluid ports = 80 lead - 10 lead for not-needed normal blocks = 70 lead
6 distributors ~ 190 Tin, 68 Iron, 8 copper, 12 glass (This is for 7, but it'll be proportional, I'll do the same next)
Ordered High-distributor reactor:
3 fluid ports = 30 lead
(not enough blocks replaced to reduce lead need directly)
18 distributors ~ 570 tin, 204 iron, 24 copper, 36 glass
The driver is definitely TIN. I haven't looked for reduced rates when using 1 return, then replacing 2 feeds with Weighted distributors.
I don't know the spawn rates for various items. I've been mining a 100x100 block with a miner from height 49 or so; this should give SOME idea of how hard it is to get lead vs tin.
I was nearly out of both lead and tin when I finished my reactor, perhaps 4 lead and 100 Tin total.
I currently have 57 lead and 205 tin, or about 81% of lead needed and 36% of tin needed to do this again. It is favorable to do this again with Lead.
If you factor in a second reactor housing, it is likely better to do this with Tin to help save the total 230 Lead to make a second fluid reactor. (60 for the reactor, 170 for the fluid vessel)
If comparing in terms of UU-matter, Tin ore is about 8x cheaper than Lead ore. While I may need 365 tin vs 170 Lead, I should be able to make it with 1/4 the UU-matter (if that was what I wanted to do).