First, I don't know anything about Mitsubishi. Never owned or drove one.

But, I found a CL listing for a '91 3000GT VR4 with no exterior damage at all and although there's only 2 interior pics, it also looks perfect. Engine is apparently good, but he says 1st gear is out. This model year had the 5 speed.

How much am I looking at for this? Does this use the same transmission as the Dodge Stealth? If so that would probably make it a lot easier, as I am in the US.

Thoughts on 1st gear rebuild vs. buying a manufactured trans? What cars came with the same trans, or one that I could get parts out of?

I assume this car looks like a bit of a headache to own, but it looks like a good headache

 

They are becoming a sought after collectors car.

3KGT/GTO and the Dodge Stealth are similar..just different exterior styling. The VR4 and the R/T are the same.

You could get the transmission rebuilt and most likely upgraded. Jacks transmission can rebuild it and even make is stronger.
3S AWD Transmission Build Services ? Jacks Transmissions

They are a little hard to work on since the motor bay is cramped but with patience you can. They are definitely cool cars and I owned one I would keep it relatively stock with mild upgrades on the engine.