Adding a plasmid to E.coli is absolutely routine work and you wouldn't need much fancy equipment for that. But that is very far from creating bioweapons. Plasmids are not integrated into the genome, they stay separate.

For viruses you'd need cell cultures of human cells, they're much more sensitive than E.coli. If you don't have sterile working conditions there you'll fail.

And you can't add plasmids to viruses, so you need to integrate your changes into the actual virus genome. I don't actually know how difficult that is, but it is certainly a lot more difficult than plasmids into bacteria.

The $100M lab in that Twitter thread is what they think would be needed for AI to develop new viruses. So the main argument there would be that a lot of actual experiments would be needed, not just theoretical calculations. And if AI is supposed to do them, it needs to be able to run experiments which requires automation.

If you're only looking for a generic virus for terrorist attacks, just get some Ebola. There's an outbreak right now, so it should not be too difficult. And it's plenty scary already, even if it isn't as dangerous in a first world country with proper reactions to an outbreak as a hypothetical designed bioweapon.