If you'd like to hear how a classically trained singer treats folk material, try Richard Dyer-Bennett (only two recordings of him on CD, but probably more will be re-issued). Or Peter Pears, along with Benjamin Britten.

If you want to hear real traditional material, there's probably more recordings available than there ever have been. (CAMSCO can get any or all of them for you---pick a general style or area of interest)