There are 3 colleges and universities that could match your wishes
(less than $25,000 a year expenses, IR as a major, African Studies as
a minor). I'll later disclose my search strategy, so you can try to
match the search better to your needs (if you are minority, or an
athlete, or could get some sort of financial aid; or if I didn't get
you and you want the degree to be $25,000 for the four years...).
State University of New York College at Brockport
Offers a programme in "International Studies" as well as a minor in
Out-of-State students pay approx. $11,553 in tuition, and you have to
add to that some $10,000 in dorms, and other living expenses.
University of Kansas
Offers a programme in Political Science that includes IR (you can also
take it as a co-major), as well as a minor in African Studies.
Out of State students pay some $13,866 in tuition fees, and should
expect some $9,000 in living expenses.
Western Michigan University
Offers a programme in International and Comparative Politics, and a
minor in something they call "Africana" studies, which includes
African Studies as well as African-Diaspora / African-American
Out of State Students pay $15,856 in tuition fees, and some $7,000
more in dorms and other living expenses.
Now, this is suppose to answer your question. However, let me dispatch
some personal advices, since my academic route was not dissimilar to
the one that you plan to take:
(1) My search strategy: I used the search engine on the site College
Board.com to get universities in the West Coast (I excluded only Ohio,
California, Oregon and Washington), with fees less than $25,000 (or
about that amount, as you see, it is not cheap), and that have IR as a
major. You can "play" with this search engine: adding states, amending
the fees that you're willing to pay, adding or changing majors, etc. :
Find a College - Search Engine
(2) International Relations sounds very glamorous, but the truth is,
that IR theories are based on Political Science ones, and that you
will be studying a lot of Political Science in any case. My advice to
you, if you see that this limited list of colleges, is to try also
with colleges that offer Political Science.
(3) Try to see if you can apply - for one reason or another - for
financial aid/grant. I am pretty sure that the field of African
Studies has to offer some scholarships to students who are eligible.
(4) This might not be a full list, since African Studies minors are
sometimes hard to find, hiding behind such definitions as "Area
Studies". I recommend, that you'll check all schools that offers IR as
a major, as they are registered with the college board, so you might
find something I haven't.
I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it.