My idea about railgun economy would be, if the statement about single-shot railguns being superior in every aspect to multiple-shot railguns is true, this:
Less shot railguns should generally take up less space, and resources. As a single entity, that is.
More shot railguns are more bulky, but more efficient overall, especially when mass-produced. Think of it as this way - you don't need more components for a single multiple barrel weapon, than several single barrel weapons.
Right now it looks like this:
10cm Railgun V10/C1/S1
Damage Per Shot (1) 1 Rate of Fire 5 seconds Range Modifier 10,000
Max Range 10,000 km Railgun Size 0.975 HS (49 tons) Railgun HTK 0
Power Requirement 0.75 Recharge Rate 1
Cost 0.9 Crew 3
Development Cost 67 RP
Materials Required
Duranium 0.2
Neutronium 0.5
Boronide 0.2
And 4 shot:
10cm Railgun V10/C1
Damage Per Shot (4) 1 Rate of Fire 15 seconds Range Modifier 10,000
Max Range 10,000 km Railgun Size 3.0 HS (150 tons) Railgun HTK 1
Power Requirement 3 Recharge Rate 1
Cost 1.7 Crew 9
Development Cost 92 RP
Materials Required
Duranium 0.3
Neutronium 1.0
Boronide 0.3
...
Wait a minute, who said that multiple shot railguns are worse in every aspect? They still require less resources than 4 single shot railguns...
Still, what I propose is this:
10cm Railgun V10/C1/S1
Damage Per Shot (1) 1 Rate of Fire 5 seconds Range Modifier 10,000
Max Range 10,000 km Railgun Size 1 HS (50 tons) Railgun HTK 0
Power Requirement 1 Recharge Rate 1
Cost 1 Crew 3
Development Cost 67 RP
Materials Required
Duranium 0.2
Neutronium 0.5
Boronide 0.2
and 4 shot:
10cm Railgun V10/C1
Damage Per Shot (4) 1 Rate of Fire 15 seconds Range Modifier 10,000
Max Range 10,000 km Railgun Size 4-0.32=3.68 HS (184 tons) Railgun HTK 1
Power Requirement 4-0.32=3.68 Recharge Rate 1
Cost 4-0.32=3.68 Crew 12-0.96≈11
Development Cost 92 RP
Materials Required
Duranium 0.8 - 0.064 = 0.736
Neutronium 2.0 - 0.16 = 1.84
Boronide 0.8 - 0.064 = 0.736
Basically, every additonal shot reduces the price in materials, power requirement and size by 2%.
I also suggest that it would be... better, to have a separate technology line for more shot railguns, which means that 1 shot railgun is the default starting technology. But, who said you can't make a 100-shot railgun? Well, have theoretical designs for it, at least?
We might encounter a problem with this - with so many shots, you'd eventually make that 2% into a 100% and more, which could result in the builder getting resources... So, I offer either - make diminishing returns after... 10 shots? Meaning you'll no longer get as 2% but 1.98%; 1.96% etc... Or, set the hard limit to 25%. Personally, I'd prefer a diminishing returns approach, if it's not too hard, at least.
This is the rough idea about the economy behind it. Perhaps more values can be tweaked? Maybe that 2% has to be a different number?
Still, a fantasy of 1000-shot railguns being achievable would be nice...