Note that qualifications from the Open University (http://www3.open.ac.uk/study/postgraduate/education/index.htm) and the Institiute of Education (http://www.ioe.ac.uk/study/masters/105.html) (and probably distance enducation providers) typically do things in a modular way. Therefore you don't necessarily have to commit to a whole Masters up-front. You may be able to just study one module that teaches what you most want to know now. That lessens the financial commitment somewhat.
Also note that Nottingham (the town given in your profile) is an OU regional centre (http://www3.open.ac.uk/contact/maps.aspx?contactid=5). If you contact them, you might be able to drop in some time and have a look at some of the teaching materials from the MA in online and distance education, and get a better idea whether what is taught is what you want to learn, and discuss the time and financial commitments.
Finally, note that a few bits of material from the MA are on OpenLearn: http://openlearn.open.ac.uk/course/category.php?id=5&perpage=20&page=2