Secondary Teacher Certification?

I graduated with my B.A. in French from a state school in Iowa in 2009. I am from Illinois. For the past 2 years I have been teaching English in France for the French Ministry of Education. I plan on returning to the States soon to become a certified high school French teacher. However, I am a bit lost as to the certification process. I already have a Bachelor's degree- but no certification, just my 2 years experience of teaching English abroad. Could someone break it down simply for me? Do I need another degree or can certification consist of night classes/not full-time school. Also, is teacher certification expensive? Thanks in advance.