Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

SCC, you might consider dropping the TL of one of the more advanced drive systems and/or advancing the TL of the society in that area, so that you can use antimatter rockets or total conversion or whatever you need to get back and forth in a reasonable time. This also makes it cheaper, so that there is a margin for wasteful practices like import bans on crop seeds, and you can introduce the in-continuity reason for them when you come up with one.

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

That would require super science, something OP doesn't want.

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

Actually things are probably within tolerable at the moment. I'm getting $20 per pound shipping.

And anti-matter doesn't work like that. In fact it's not a fuel, you lose too much energy in the annihilation event (Most of it isn't easily usable)

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

Unless you have some way of directing all those neutrinos. But even optimal production would take loads more money than any other type of power.

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

It's not just neutrinos, it's well, everything. Antimatter annihilation does produce the E=(2)MC^2 energy, but not in a convenient form

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

Antimatter-powered neutrino drives aren't necessarily superscience, but they are like TL11 or 12.

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

No the no trade possible argument. Unless the colony ships are one-way affairs the ships will be making round trips and it won't be long before someone decides that them coming back empty isn't the best idea

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

But why would the colony ships not be one-way affairs?

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

Because it's not cost effective. Then there's the added problems of how you break down the spaceship (Likely still in orbit) and what you do with it once you've broken it down (Most of it's hull is/was metal).

And once the ship is in orbit around the colony planet all it needs is a re-fuel and enough food to see the crew home for it to make a return trip. Given that I'm putting Open Spaces so that I've got total life support, meaning no food or other crew consumables are need, and Magsails, which need no fuel, there's no good reason NOT for them to make round trips

Re: [Space/Spaceships] Getting the velocity/Delta V I want with the tech I want
 

...Because the fuel would be massively expensive? Though you seem to have concluded otherwise on the basis of calculations you're keeping to yourself.