Cost, of course, is a relative thing. Check out eLearners for more info about other recognized universities.

Otherwise, it only helps you get a promotion at your existing job. I don't think many employers give it as much weight as a traditional degree from a traditional university.

From memory:

* East Carolina University http://online.northcarolina.edu/program.php?id=185
* U Hawaii Manoa http://www.hawaii.edu/uhmmusic/degrees/MA_MusEd_Online.htm
* Boston U (also has the DMus in Music Ed online) (has a reputation for being excellent – and very demanding) http://musiceducation.bu.edu/
* U Montana (hybrid)
* Duquesne (hybrid)
* U South Florida http://www.ecampus.usf.edu/
* Stephen Austin
* U Southern Mississippi http://www.usm.edu/southernmissonline/programs/musiceducation.php
* U Northern Iowa (hybrid, in-state)
* Auburn U.

Google for "[school] online master music" and watch out for the commercial sites.

None of these is intended for initial certification though. One option you might want to try is getting certified elementary grades general (such as via Western Governor's) through a post-baccalaureate initial certification program (a Bachelor of Music or BA in Music is often sufficient undergrad for elementary grades general certification) and then either doing an MME online or simply following your state's requirements for an add-on area once you have the elementary certificate. I've seen this work well for a few BA Music folk that didn't want to get a full BME. http://www.wgu.edu/education/teacher_certification_elementary_program

The only real challenge to getting an add-on in K-12 music is the methods classes if you didn't take those in undergrad. You'll have to find a school to do those in on-site because they aren't very well suited to online instruction. You'll need brass, woodwind, string, percussion, and voice methods from somewhere either route you take.

If you're planning to enter the field of public school music teaching – know that far more than half have a master's degree (competition for those jobs is steep) and that music is rarely a shortage teaching area in any school district.

Good luck.