*For the record, and not to get too personal, that is in fact the exact road I went down (going to an expensive school that was particularly well-known for producing PhD students, with an eye towards becoming one myself), though I realized too late that academia was not going to happen for me. Ergo I very much don't exactly take kindly to the suggestion that I deserve debtor's prison for decisions I made when I was 16/having to change gears. Thanks.
Well, I, actually, went to a non-prestigeous private undergraduate residential college, which would have been expensive, but I got a scholarship (I was not even eligible for any of those nice loans, being a foreigner - and I had exactly no money to pay cash). Out of, literally, thousands of students in my graduating class, exactly 3 went for a ph.d. (and that was considered a very successful year in this respect). Nobody had gone for a Ph.D. in my field from that school in years. It was not at all a problem getting admitted to a good grad school - with full funding. You do NOT have to go to a prestigeous undergraduate school to get to a pretty good doctorate program. You just have to be decent and know what you want.
Anyway, if you want to go for a ph.d. in economics in the US, just learn Spanish and come down for your undergraduate to us here in Mexico. We charge less than USD$10 grand a year and send more students for a US ph.d. than all but a handful schools in the world. And living costs here are low