There are very few opportunities indeed for making a living out of the study of folk music, but I do know a very few people who sort-of manage it; mostly as part of their work as university lecturers. Most of us have to fit it into whatever time is left over from the day job, and typically it costs us more than we ever make out of it. A labour of love, really.

So far as published resources are concerned, there are plenty; though most are out of print, some of the older ones are becoming available online, nowadays largely via Google Books and the Internet Archive. Others can be got second-hand; http://www.bookfinder.com/ is a useful meta-search engine that indexes the current stocks of a great many dealers.

There is a useful bibliography by David Atkinson, concentrating on English material, at http://www.efdss.org/songbib3.pdf, and no serious researcher should try to get by without The Roud Folk Song Index. Also at the Vaughan Williams Memorial Library website is Roud's own bibliography of works consulted and/or indexed, and indexes of several important manuscript collections.

There is a lot more to be found, of course, and looking round in the Forum here will get you plenty more leads. I'll also just mention a list of Internet resources at http://www.folk-network.com/directory/links.html; it's rather out-of-date at present, but nevertheless contains a lot of useful links.