You've already mentioned your best option.  It doesn't get any faster or cheaper than CLEP exams...and the military is a big supporter of CLEP exams.  They push those things a lot. 

There are CLEP exams which are worth six credit hours, so your best bet is to pick a subject that you are good at, spend a little time studying for the exam, and then spend the $80 and take the test.  It doesn't get any better than $80 for six credit hours.  A great study resource is www.instantcert.com  It's 20 bucks a month, but it shouldn't take longer than a month to study for the exam.  So, for a total of $100, you could have six credit hours and be well on your way to getting the job you want in the Air Force.

I was in the Navy and took the ASVAB test before enlisting.  I don't remember my score, but apparently I did very well because the recruiter was practically salivating and trying to get me enlisted in the nuclear power program.  But, my interest was in journalism and broadcasting, so I spent five years working as a Navy journalist.   I had good times and bad in the military, but I wouldn't trade the experience for anything in the world.