Hi there! Glad to hear you are taking an interest in these questions. I wanted to offer you a few general observations that might be helpful.

arguments against institutions like GiveWell that focus on giving away bednets, that talk about how it ends up making these communities dependent on donations and unable to produce their own bednets.

I think a few different questions might be getting linked together here. One question is the best way to get people an effective public health intervention, like malaria nets. Another is how we can ensure economic development, so that communities need not be dependent on foreign support. 

To answer the first: from my perspective, there’s no reason any particular community needs to be able to make their own malaria nets. Rather, they should be a made by whoever has a comparative advantage in making malaria nets. It would be highly inefficient if every community threatened by malaria needed to make their own nets. That's why we trade. So I'm not sure about an argument that would require we need to teach any malaria stricken community how to make nets themselves.

But that does lead to the second question: of how a community can become economically self sufficient. This is a much more difficult question—in fact it’s one of the big questions of economics, particularly developmental economics. 

My understanding (noting this is a huge subject) is that we don’t know of any silver bullets, but it’s well-accepted that better health, education, and institutions is a key part of the story. Because we don't have a silver bullet, we can at least offer to alleviate a preventable health problem like malaria. Hopefully, a healthier society will create the foundation for future prosperity and wellness--so that they won't be dependent on donations. In particular, when the long term effects of malaria nets have been looked at, they've been highly effective in reducing the overall mosquito population.

This also means that mosquito nets have 'positive externalities'. That is to say, they help people beyond the purchaser of the net. When goods have positive externalities, they tend to be undersupplied. That might help explain why communities aren't already trading for more malaria nets, as well as the need for subsidy. 

Also: I worry a bit about the word 'sustainability' in these contexts. One might have to, say, runaway from a mugger at an unsustainable pace, but that's alright because it's an exigent circumstance. You aren't going to be running forever. 

I think when we say 'unsustainable' we usually mean something has negative externalities, like carbon emissions, so we can't keep on the same path for ever. But there are plenty of temporary measures that are at once unsustainable but certainly worth doing. I agree with you we should focus on which actions will have the best long run consequences. But that doesn't necessarily mean sustainable. 

One last thing: Your point about weak currencies is very thoughtful. You might want to investigate the concept of purchasing power parity and Will MacAskill's concept of the 100x multiplier. 

Hopefully someone else can give further details about malaria nets or GiveWell, if you are curious to learn more!