I believe choosing a course you are interested in is more important. Since you mentioned you really like economics, go with your heart.

As for Cornell vs SMU, finances aside, I'll definitely recommend Cornell. I'm from SMU btw. SMU's education is good in itself, but studying in a foreign university would greatly expand your world view. And Cornell's Ivy League. I don't know if you have already applied, but LSE has cheaper tuition fees than Ivy League and, to me at least, their programme is more prestigious.

As for finances, if your parents can afford it, albeit minor strains on their finances, you should still pursue the better course. Discuss it with them. Of course I believe one should be self sufficient, so you might want repay them in installments and with interests after you start work so you won't feel that bad about straining their finances.

US universities are very generous with financial aids, although in recent years they are cutting down the amount given to foreigners. You might want to find out more information on this.