...exploiting the lowest paid populations on the planet, without offering them even half of what they would pay an American
I think you're coming from a good place, but there are a number of issues with your views...
First, in terms of cost of living, an Indonesian employee would only need 1/4 what the American would. So, I guess a "national" minimum wage of $1.81 instead of $1.17 would be "fair"?
Also, do you have proof that laborers in these factories are making only minimum wage or is that just an assumption?
As for "affording" the product they produce, things aren't that simple. First, they have their own market with brands and models that aren't available to us in the U.S. There aren't even Epiphone dealers in Indonesia, as far as I am aware.
In the UK, the guitar linked by the OP is 1299 GBP, which is $1600 USD.
In other parts of Europe, it's 1399 Euros, which is $1500 USD.
Also, similar products tend to cost less there, so Western countries are actually paying a premium for the same quality native Indonesians get for less. Blame capitalism
Also, to your earlier point about factory workers being 15 year old girls...I was 15 when I legally started working for minimum wage here in the U.S. Are you suggesting that the ethics would be different if I was a "girl"?