CU-Boulder does not give significant financial aid to OOS students. Neither does UIUC.
My DH has a PhD in physics from a top 5 physics program. My SIL also has a physics PhD and is currently a tenured physic prof at a top U. Dh’s classmates in grad school didn’t come from “elite” undergrad programs. They came from places that include Drexel, Bucknell, Penn State, University of Maryland, Haverford, Arizona State, New College-Florida, Florida State, Colorado School of Mines, University of North Dakota, Michigan State and OK, there was one guy from Brown…you get the idea.
There is nothing magical about your list of undergrad colleges. In fact the LAC (Colby) on your list is probably a poor choice for an ambitious physics student. (I’ll get to why later.) The undergrad physics curriculum is pretty standardized across the board at all US colleges & universities. So the basic coursework isn’t going to differ much no matter what undergrad you attend. What you should be looking at is research opportunities in your area(s) of interest as well as the breadth of upper level electives offered in math, physics, chemistry and computer science. The opportunity to take some graduate level classes while still in undergrad is also a huge plus.
LACs have limited research options, and they do not offer a variety of upper level specialized electives. Both issues are the top complaints I’ve heard over and over from physics students who have pursued grad studies. (The other issue you’ll run into at a LAC is the limited physics faculty. Upper level elective are only offered every other or every third year. You will probably have the same prof for several classes–which can be a great way to get to know your profs well, but the down side is that it’s pretty much a sure thing that for some of those classes, the prof is teaching outside their area of expertise. Also if any prof is poor teacher–there’s no getting away from them. )
What PhD programs look at when considering grad applicants is: grades in upper level math & physics electives, GRE score (esp the quantitative portion), your research experience and LORs from your physics profs. (The academic physics community is a lot smaller than you think. Seriously the academic physics world is tiny. Everyone knows everyone. So when your research advisor writes a LOR that says “this kid walks on water, best student I’ve ever had,” top programs pay attention–even if you are attending Never Heard of It College.)
You’ve been offered a great deal at UNC. Take it. Do well in your classes, find an interesting research lab and get involved, impress your profs, kill your GRE. Do all that and no grad physics program in the US will be beyond your reach.