I don' think there are many 'short' courses that are around 6 months. If you are doing a shorter course to find out if you like massage, I would suggest maybe doing a taster course first of all and then register for a proper course if massage is something you'd like to learn. If you do an Adult Education course these tend to run Sept - Jul. However there are plenty of course providers that run for a set number of weekends over so many months.
Depending on what you want to do once you're qualified may help you to decide which qualification you opt for i.e. if you want to work abroad then maybe an ITEC course is more suitable. However there are many accredited courses that are equally as good.
Also, expensive courses do not mean it is a better course. I would also do research on the company and the trainer. Adult Education courses tend to be competitively priced and are usually good courses.