There are a lot of options out there for you, and it should be more your choice than ours since you'll be the one looking at it every day. If you want, you can let me know how you want it to look and how many fans and what-not, and I can find you a couple to look at and we can go from there.
Its definately possible to get you a case under $100. Do you like the white or do you not mind for color? I've personally had good experience with NZXT for airflow and expansion, but they usually go right for $100.