American student going for non-American PhD?

[heyo]

Does anyone have experience or input in this area? I graduated from a US university for undergrad, and I've already applied for some PhD programs in the US. I'm prepared for the outcome where I don't get into any of them, and I've been considering all options. I've decided that the PhD won't be worth it to me if I have to pay for it, or if my prospects afterwards would not be great (if I went to Podunk U., say)

 

I forget exactly how I came upon it, but I found that there is basically a lot of stuff going on in my research interests/area (robotics, specifically) at Seoul National University, and I've started to consider it. At the same time, I wonder what my prospects would be having received a PhD (or say, a Masters only) from there or from other universities outside of the US. I don't hear much of US students leaving the country for post-graduate work.