Wayland Baptist University http://www.wbu.edu/academics/online_programs/dpo/mah.htm 37 credits required @ $312. This seems very flexible. The price is comparable to AMU and it's from a B & M school. This looks pretty good.
Wayland Baptist is a well respected private Texas university and very competitive regarding their online tuition. From the State supported side ... Sam Houston State University offers an online Master of Arts in History degree program that encompasses topics that include early American History and military History. http://www.shsu.edu/gradcat/his.html
Also from the Great State of Texas, Southwestern Assemblies of God University offers a Master of Arts in History and the University of Houston Victoria offers a Master of Arts in Interdisciplinary Studies with History concentration.
In the meantime, we've got the Union Institute's PhD in Humanities & Culture, Harrison Middleton University's DA in Humanities & Social Sciences, and a few dissertation-only docs.
Yes, Union is RA: http://www.myunion.edu/about/accreditation.html Info on their "Ph.D. Program in Interdisciplinary Studies" is here: http://www.myunion.edu/academics/cohort/humanities-culture.html It does have residency requirements though: "The Cohort Ph.D. program uses a hybrid and distributed model for program delivery. The academic year for the Cohort Ph.D. program is divided into two six-month terms: January 1 to June 30 and July 1 to December 31. At the beginning of every January and July new and returning learners come together for nine days at an academic residency. The learners move through the doctoral program as members of cohorts that are formed within and across the program’s three areas of concentration and are determined by the date of the Initial Academic Residency." From their FAQ here: http://www.myunion.edu/academics/cohort/faqs.html
Union is RA through the North Central Association. Harrison Middleton is NA through the Distance Education and Training Council.