Thanks for the reply!
Yes, Illinois is definitely cheaper, tuition-wise about $10,000 less than MIT, but I've saved up enough that I would be able to manage either program financially without having to take out loans. In terms of ranking, I've seen it swing either way. I've heard that UIUC is the more traditional program and where a lot of US structural engineers come out of. Their structures department is definitely larger than MIT's with more professors that have had experience as professional engineers. MIT, on the other hand, is still a very well regarded program and definitely prestigious in engineering in general. Location-wise I would prefer Boston/Cambridge over middle-of-nowhere-Illinois. MIT also seems to have a more creative approach to the program with collaborative design projects and such (though very intense combination for a 9 month period), whereas Illinois is course-work only. I also feel like MIT might be more marketable for when I'm applying for jobs, but that's only a guess on my part considering MIT's prestige factor.