The Study Portal https://www.shortcoursesportal.com/search provides links to short courses. These can be refined by subject/cost etc.
https://www.futurelearn.com has links to free short courses from Universities around the world. These can be linked together to build a ‘pay as you go’ qualification if required. Courses can be started at any time and are also listed on individual university websites.
http://www.open.edu/openlearn/free-courses lists free courses provided by the Open University. Study hours range from 1 to 84 and courses can be started at any time.