Hello, I've been researching modern slavery at Founders Pledge recently. (Also oops, pressed send before I meant to- hence the edit!)

I really respect the Freedom Fund for pushing forward with evaluative work, esp in an area where there aren't many published evaluations  (you can see one of their evaluations here). At the same time, I think the $657 figure is very optimistic. My understanding is that the figure GWWC are pulling from (the $657 amount) is based on weaker, observational evidence—and doesn't really account for the marginal funding amount. By this, I mean that I expect that most high-quality programs would be funded within the next few years (so this is really the cost to speed this process up).

My general sense is that this is an area where the evidence basis for direct work is suprisingly weak; there are hardly any RCTs, or strong quasi-experiments. It's true that modern slavery interventions are difficult to test, but nonetheless this is pretty striking given that modern slavery is an area that's of increasing interest to many policy makers (e.g. movement towards an EU ban on products made with forced labor, SDG goal 8.7). 

I suspect the lack of RCT-style evidence, and the sense that it's not super neglected, might be why there hasn't been much EA focus here. Nonetheless, I think focusing on interventions around advocacy, tech and research may be promising here (and I'd probably argue for prioritising this over direct work, given current funding patterns). 

Advocacy in this area can push for things like strengthening existing Modern Slavery Acts (e.g. by adding sanctions, existing legislature is very weak) and bringing in 'floor wages' for workers (e.g. see this video from the Asia Floor Wage Alliance). Tech developments to actually be able to locate modern slavery seem critical to me, and like a key bottleneck in this area: to NGOs (who need to be able to prioritise their efforts, measure the impact of their work and so on), to multi-national companies (who need to be able to locate modern slavery within their supply chains, in order to choose contractors who do not use modern slavery), to consumers (to know which products are at risk of modern slavery and apply consumer pressure), and to strengthening legislation (it seems difficult to impose sanctions on multi-national companies, if companies can genuinely argue that they don't have the ability to locate modern slavery in their supply chains). I'm also interested in tech work that helps workers stay safe as they migrate (e.g. apps that provide accurate job info, tell people their work rights, etc etc). So I'd probably lean to charities with a strong focus on this; afraid I don't have a one-stop recommendation yet as work is still in progress, but you might want to check out the Asia Floor Wage Alliance, Global Fund to End modern Slavery, Anti-Slavery International and International Justice Mission as well as the Freedom Fund (for groups that also have an advocacy/ tech focus).