Well, getting durned good grades surely doesn't hurt...use what resources you have wisely. Take advantage of contacts. While the wealthy may seem to have an advantage here, it is not necessarily so.
SAT and GRE (or GMAT, LSAT, MCAT, etc) prep can be done on your own, without the need for those expensive classes. Buy a book (or 2 or 3) and start practicing soon!
I think that you still will have to save your pennies to apply to colleges. There isn't really a way around this. Application fees are high. If you are of limited means, start early. Talk with entrance counselors from lots of universities. Don't be afraid to ask what they can do for you.
On the average, state universities will provide the best education. Some really good public universities are in California (10 UC and 23 CSU campuses), Oregon, Ohio, Michigan, New York (64 campuses!), etc...
UC Berkeley and Los Angeles have oodles of programs that are very highly ranked nationally. They compete very well with Ivy League and other private schools, especially in graduate studies. Considering that the costs are so much smaller, you can't go wrong...
While public institutions have low costs, many private insitutions will give full scholarships to deserving students. So do not overlook the private university. I had a friend who was denied admission to UCLA and UC Berkeley, but was awarded a full scholarship at Boston University. You may find that there is less competition for admission to private universities.
When I was applying for college, the internet was a fledgling, with maybe a few message servers and a few webpages. The amount of information on the net now is staggering...USE IT! Access is also improved now, as you can log on at public libraries and many other places (i.e. internet cafes, which are relatively cheap). Do your homework!
cellmould